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 $164.31   8.227%   $177.8278   $177.83   $177.85   $177.80  
  Purchase #2 $57.30   5.325%   $60.3512   $60.35   $60.35   $60.40  
  Purchase #3 $102.50   8.812%   $111.5323   $111.53   $111.55   $111.50  
  Purchase #4 $72.73   12.522%   $81.8373   $81.84   $81.85   $81.80  
  Purchase #5 $182.85   13.861%   $208.1948   $208.19   $208.20   $208.20  
  Purchase #6 $186.70   4.401%   $194.9167   $194.92   $194.90   $194.90  
  Purchase #7 $188.79   13.296%   $213.8915   $213.89   $213.90   $213.90  
  7 purchase totals = $955.18       $1,048.5516   $1,048.55   $1,048.60   $1,048.50