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 $76.87   13.549%   $87.2851   $87.29   $87.30   $87.30  
  Purchase #2 $209.56   4.756%   $219.5267   $219.53   $219.55   $219.50  
  Purchase #3 $45.39   7.796%   $48.9286   $48.93   $48.95   $48.90  
  Purchase #4 $22.71   8.711%   $24.6883   $24.69   $24.70   $24.70  
  Purchase #5 $139.96   10.350%   $154.4459   $154.45   $154.45   $154.40  
  Purchase #6 $93.77   3.162%   $96.735   $96.74   $96.75   $96.70  
  Purchase #7 $110.78   4.366%   $115.6167   $115.62   $115.60   $115.60  
  7 purchase totals = $699.04       $747.2263   $747.25   $747.30   $747.10