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 $84.53   11.343%   $94.1182   $94.12   $94.10   $94.10  
  Purchase #2 $8.57   5.838%   $9.0703   $9.07   $9.05   $9.10  
  Purchase #3 $118.87   6.800%   $126.9532   $126.95   $126.95   $127.00  
  Purchase #4 $211.63   7.225%   $226.9203   $226.92   $226.90   $226.90  
  Purchase #5 $10.39   10.862%   $11.5186   $11.52   $11.50   $11.50  
  Purchase #6 $136.36   10.240%   $150.3233   $150.32   $150.30   $150.30  
  Purchase #7 $105.93   6.488%   $112.8027   $112.80   $112.80   $112.80  
  7 purchase totals = $676.28       $731.7066   $731.70   $731.60   $731.70