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 $61.74   11.246%   $68.6833   $68.68   $68.70   $68.70  
  Purchase #2 $100.77   6.469%   $107.2888   $107.29   $107.30   $107.30  
  Purchase #3 $142.76   7.266%   $153.1329   $153.13   $153.15   $153.10  
  Purchase #4 $91.30   11.684%   $101.9675   $101.97   $101.95   $102.00  
  Purchase #5 $60.64   4.475%   $63.3536   $63.35   $63.35   $63.40  
  Purchase #6 $99.44   10.506%   $109.8872   $109.89   $109.90   $109.90  
  Purchase #7 $238.67   8.404%   $258.7278   $258.73   $258.75   $258.70  
  7 purchase totals = $795.32       $863.0411   $863.04   $863.10   $863.10