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 $123.95   6.501%   $132.008   $132.01   $132.00   $132.00  
  Purchase #2 $230.95   7.229%   $247.6454   $247.65   $247.65   $247.60  
  Purchase #3 $45.39   13.155%   $51.3611   $51.36   $51.35   $51.40  
  Purchase #4 $131.71   8.606%   $143.045   $143.05   $143.05   $143.00  
  Purchase #5 $25.81   13.358%   $29.2577   $29.26   $29.25   $29.30  
  Purchase #6 $53.99   7.282%   $57.9216   $57.92   $57.90   $57.90  
  Purchase #7 $105.35   8.151%   $113.9371   $113.94   $113.95   $113.90  
  7 purchase totals = $717.15       $775.1759   $775.19   $775.15   $775.10