Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $191.98   5.816%   $203.1456   $203.15   $203.15   $203.10  
  Purchase #2 $242.51   11.819%   $271.1723   $271.17   $271.15   $271.20  
  Purchase #3 $93.73   12.144%   $105.1126   $105.11   $105.10   $105.10  
  Purchase #4 $152.89   7.789%   $164.7986   $164.80   $164.80   $164.80  
  Purchase #5 $117.96   10.299%   $130.1087   $130.11   $130.10   $130.10  
  Purchase #6 $179.59   10.172%   $197.8579   $197.86   $197.85   $197.90  
  Purchase #7 $176.34   12.623%   $198.5994   $198.60   $198.60   $198.60  
  7 purchase totals = $1,155.00       $1,270.7951   $1,270.80   $1,270.75   $1,270.80