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 $62.51   11.826%   $69.9024   $69.90   $69.90   $69.90  
  Purchase #2 $148.91   11.557%   $166.1195   $166.12   $166.10   $166.10  
  Purchase #3 $113.44   13.513%   $128.7691   $128.77   $128.75   $128.80  
  Purchase #4 $165.43   7.836%   $178.3931   $178.39   $178.40   $178.40  
  Purchase #5 $123.79   4.770%   $129.6948   $129.69   $129.70   $129.70  
  Purchase #6 $117.31   13.753%   $133.4436   $133.44   $133.45   $133.40  
  Purchase #7 $15.68   12.604%   $17.6563   $17.66   $17.65   $17.70  
  7 purchase totals = $747.07       $823.9788   $823.97   $823.95   $824.00