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 $52.27   13.151%   $59.144   $59.14   $59.15   $59.10  
  Purchase #2 $24.44   9.403%   $26.7381   $26.74   $26.75   $26.70  
  Purchase #3 $6.32   7.102%   $6.7688   $6.77   $6.75   $6.80  
  Purchase #4 $118.99   4.474%   $124.3136   $124.31   $124.30   $124.30  
  Purchase #5 $152.34   10.812%   $168.811   $168.81   $168.80   $168.80  
  Purchase #6 $149.91   5.532%   $158.203   $158.20   $158.20   $158.20  
  Purchase #7 $102.56   4.314%   $106.9844   $106.98   $107.00   $107.00  
  7 purchase totals = $606.83       $650.9629   $650.95   $650.95   $650.90