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 $34.94   8.591%   $37.9417   $37.94   $37.95   $37.90  
  Purchase #2 $232.91   6.467%   $247.9723   $247.97   $247.95   $248.00  
  Purchase #3 $99.47   12.296%   $111.7008   $111.70   $111.70   $111.70  
  Purchase #4 $29.39   12.140%   $32.9579   $32.96   $32.95   $33.00  
  Purchase #5 $180.63   4.295%   $188.3881   $188.39   $188.40   $188.40  
  Purchase #6 $226.94   4.267%   $236.6235   $236.62   $236.60   $236.60  
  Purchase #7 $95.73   6.552%   $102.0022   $102.00   $102.00   $102.00  
  7 purchase totals = $900.01       $957.5865   $957.58   $957.55   $957.60