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 $149.34   12.319%   $167.7372   $167.74   $167.75   $167.70  
  Purchase #2 $180.87   8.333%   $195.9419   $195.94   $195.95   $195.90  
  Purchase #3 $167.89   5.529%   $177.1726   $177.17   $177.15   $177.20  
  Purchase #4 $235.73   7.691%   $253.86   $253.86   $253.85   $253.90  
  Purchase #5 $178.85   12.692%   $201.5496   $201.55   $201.55   $201.50  
  Purchase #6 $172.47   10.804%   $191.1037   $191.10   $191.10   $191.10  
  Purchase #7 $28.28   4.603%   $29.5817   $29.58   $29.60   $29.60  
  7 purchase totals = $1,113.43       $1,216.9467   $1,216.94   $1,216.95   $1,216.90