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 $95.61   10.467%   $105.6175   $105.62   $105.60   $105.60  
  Purchase #2 $187.39   11.543%   $209.0204   $209.02   $209.00   $209.00  
  Purchase #3 $92.25   6.532%   $98.2758   $98.28   $98.30   $98.30  
  Purchase #4 $98.38   8.517%   $106.759   $106.76   $106.75   $106.80  
  Purchase #5 $49.48   11.745%   $55.2914   $55.29   $55.30   $55.30  
  Purchase #6 $189.70   12.644%   $213.6857   $213.69   $213.70   $213.70  
  Purchase #7 $13.74   10.801%   $15.2241   $15.22   $15.20   $15.20  
  7 purchase totals = $726.55       $803.8739   $803.88   $803.85   $803.90