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 $75.79   11.104%   $84.2057   $84.21   $84.20   $84.20  
  Purchase #2 $226.84   6.228%   $240.9676   $240.97   $240.95   $241.00  
  Purchase #3 $102.27   10.161%   $112.6617   $112.66   $112.65   $112.70  
  Purchase #4 $140.62   7.175%   $150.7095   $150.71   $150.70   $150.70  
  Purchase #5 $39.65   5.845%   $41.9675   $41.97   $41.95   $42.00  
  Purchase #6 $30.64   6.480%   $32.6255   $32.63   $32.65   $32.60  
  Purchase #7 $79.44   10.768%   $87.9941   $87.99   $88.00   $88.00  
  7 purchase totals = $695.25       $751.1316   $751.14   $751.10   $751.20