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 $51.76   5.511%   $54.6125   $54.61   $54.60   $54.60  
  Purchase #2 $237.42   5.657%   $250.8508   $250.85   $250.85   $250.90  
  Purchase #3 $159.76   6.761%   $170.5614   $170.56   $170.55   $170.60  
  Purchase #4 $159.26   5.696%   $168.3314   $168.33   $168.35   $168.30  
  Purchase #5 $53.45   9.597%   $58.5796   $58.58   $58.60   $58.60  
  Purchase #6 $87.89   9.461%   $96.2053   $96.21   $96.20   $96.20  
  Purchase #7 $75.68   9.462%   $82.8408   $82.84   $82.85   $82.80  
  7 purchase totals = $825.22       $881.9818   $881.98   $882.00   $882.00