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 $24.41   9.106%   $26.6328   $26.63   $26.65   $26.60  
  Purchase #2 $119.39   5.751%   $126.2561   $126.26   $126.25   $126.30  
  Purchase #3 $87.91   7.392%   $94.4083   $94.41   $94.40   $94.40  
  Purchase #4 $78.99   6.483%   $84.1109   $84.11   $84.10   $84.10  
  Purchase #5 $148.75   13.534%   $168.8818   $168.88   $168.90   $168.90  
  Purchase #6 $53.33   8.727%   $57.9841   $57.98   $58.00   $58.00  
  Purchase #7 $245.46   8.217%   $265.6294   $265.63   $265.65   $265.60  
  7 purchase totals = $758.24       $823.9034   $823.90   $823.95   $823.90