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 $106.49   11.122%   $118.3338   $118.33   $118.35   $118.30  
  Purchase #2 $191.26   10.267%   $210.8967   $210.90   $210.90   $210.90  
  Purchase #3 $242.72   5.552%   $256.1958   $256.20   $256.20   $256.20  
  Purchase #4 $173.52   10.225%   $191.2624   $191.26   $191.25   $191.30  
  Purchase #5 $65.29   11.729%   $72.9479   $72.95   $72.95   $72.90  
  Purchase #6 $114.81   11.546%   $128.066   $128.07   $128.05   $128.10  
  Purchase #7 $210.53   12.456%   $236.7536   $236.75   $236.75   $236.80  
  7 purchase totals = $1,104.62       $1,214.4562   $1,214.46   $1,214.45   $1,214.50