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 $108.93   11.314%   $121.2543   $121.25   $121.25   $121.30  
  Purchase #2 $244.53   9.579%   $267.9535   $267.95   $267.95   $268.00  
  Purchase #3 $18.76   11.513%   $20.9198   $20.92   $20.90   $20.90  
  Purchase #4 $154.34   4.574%   $161.3995   $161.40   $161.40   $161.40  
  Purchase #5 $206.59   7.135%   $221.3302   $221.33   $221.35   $221.30  
  Purchase #6 $7.83   4.852%   $8.2099   $8.21   $8.20   $8.20  
  Purchase #7 $65.35   3.157%   $67.4131   $67.41   $67.40   $67.40  
  7 purchase totals = $806.33       $868.4803   $868.47   $868.45   $868.50