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 $223.94   9.491%   $245.1941   $245.19   $245.20   $245.20  
  Purchase #2 $111.43   8.291%   $120.6687   $120.67   $120.65   $120.70  
  Purchase #3 $67.64   8.874%   $73.6424   $73.64   $73.65   $73.60  
  Purchase #4 $40.90   13.536%   $46.4362   $46.44   $46.45   $46.40  
  Purchase #5 $212.71   11.346%   $236.8441   $236.84   $236.85   $236.80  
  Purchase #6 $11.65   3.846%   $12.0981   $12.10   $12.10   $12.10  
  Purchase #7 $59.69   12.106%   $66.9161   $66.92   $66.90   $66.90  
  7 purchase totals = $727.96       $801.7997   $801.80   $801.80   $801.70