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 $86.85   6.630%   $92.6082   $92.61   $92.60   $92.60  
  Purchase #2 $145.34   8.343%   $157.4657   $157.47   $157.45   $157.50  
  Purchase #3 $68.98   11.336%   $76.7996   $76.80   $76.80   $76.80  
  Purchase #4 $40.67   13.853%   $46.304   $46.30   $46.30   $46.30  
  Purchase #5 $153.67   8.142%   $166.1818   $166.18   $166.20   $166.20  
  Purchase #6 $25.54   8.652%   $27.7497   $27.75   $27.75   $27.70  
  Purchase #7 $237.32   12.549%   $267.1013   $267.10   $267.10   $267.10  
  7 purchase totals = $758.37       $834.2103   $834.21   $834.20   $834.20