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 $56.26   4.808%   $58.965   $58.97   $58.95   $59.00  
  Purchase #2 $148.59   13.475%   $168.6125   $168.61   $168.60   $168.60  
  Purchase #3 $82.31   10.553%   $90.9962   $91.00   $91.00   $91.00  
  Purchase #4 $21.42   4.425%   $22.3678   $22.37   $22.35   $22.40  
  Purchase #5 $187.66   8.257%   $203.1551   $203.16   $203.15   $203.20  
  Purchase #6 $23.54   10.266%   $25.9566   $25.96   $25.95   $26.00  
  Purchase #7 $81.77   4.224%   $85.224   $85.22   $85.20   $85.20  
  7 purchase totals = $601.55       $655.2772   $655.29   $655.20   $655.40