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 $25.73   5.704%   $27.1976   $27.20   $27.20   $27.20  
  Purchase #2 $184.71   5.760%   $195.3493   $195.35   $195.35   $195.30  
  Purchase #3 $188.30   12.738%   $212.2857   $212.29   $212.30   $212.30  
  Purchase #4 $38.69   7.358%   $41.5368   $41.54   $41.55   $41.50  
  Purchase #5 $216.39   10.577%   $239.2776   $239.28   $239.30   $239.30  
  Purchase #6 $17.51   5.590%   $18.4888   $18.49   $18.50   $18.50  
  Purchase #7 $64.94   4.784%   $68.0467   $68.05   $68.05   $68.00  
  7 purchase totals = $736.27       $802.1825   $802.20   $802.25   $802.10