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 $142.34   6.211%   $151.1807   $151.18   $151.20   $151.20  
  Purchase #2 $87.78   4.517%   $91.745   $91.75   $91.75   $91.70  
  Purchase #3 $68.70   6.759%   $73.3434   $73.34   $73.35   $73.30  
  Purchase #4 $10.83   4.826%   $11.3527   $11.35   $11.35   $11.40  
  Purchase #5 $170.79   10.570%   $188.8425   $188.84   $188.85   $188.80  
  Purchase #6 $126.71   3.560%   $131.2209   $131.22   $131.20   $131.20  
  Purchase #7 $212.32   3.285%   $219.2947   $219.29   $219.30   $219.30  
  7 purchase totals = $819.47       $866.9799   $866.97   $867.00   $866.90