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 $48.96   3.392%   $50.6207   $50.62   $50.60   $50.60  
  Purchase #2 $154.49   12.256%   $173.4243   $173.42   $173.40   $173.40  
  Purchase #3 $70.45   3.648%   $73.02   $73.02   $73.00   $73.00  
  Purchase #4 $54.43   8.336%   $58.9673   $58.97   $58.95   $59.00  
  Purchase #5 $152.98   3.730%   $158.6862   $158.69   $158.70   $158.70  
  Purchase #6 $92.82   3.850%   $96.3936   $96.39   $96.40   $96.40  
  Purchase #7 $7.36   11.766%   $8.226   $8.23   $8.25   $8.20  
  7 purchase totals = $581.49       $619.3381   $619.34   $619.30   $619.30