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 $49.81   7.746%   $53.6683   $53.67   $53.65   $53.70  
  Purchase #2 $163.56   3.873%   $169.8947   $169.89   $169.90   $169.90  
  Purchase #3 $47.67   7.252%   $51.127   $51.13   $51.15   $51.10  
  Purchase #4 $89.42   4.612%   $93.5441   $93.54   $93.55   $93.50  
  Purchase #5 $185.71   7.751%   $200.1044   $200.10   $200.10   $200.10  
  Purchase #6 $225.95   8.439%   $245.0179   $245.02   $245.00   $245.00  
  Purchase #7 $82.88   7.310%   $88.9385   $88.94   $88.95   $88.90  
  7 purchase totals = $845.00       $902.2949   $902.29   $902.30   $902.20