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 $14.77   9.620%   $16.1909   $16.19   $16.20   $16.20  
  Purchase #2 $77.90   5.633%   $82.2881   $82.29   $82.30   $82.30  
  Purchase #3 $46.84   8.870%   $50.9947   $50.99   $51.00   $51.00  
  Purchase #4 $125.65   7.225%   $134.7282   $134.73   $134.75   $134.70  
  Purchase #5 $154.82   11.112%   $172.0236   $172.02   $172.00   $172.00  
  Purchase #6 $197.64   11.488%   $220.3449   $220.34   $220.35   $220.30  
  Purchase #7 $107.80   7.308%   $115.678   $115.68   $115.70   $115.70  
  7 purchase totals = $725.42       $792.2484   $792.24   $792.30   $792.20