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 $76.95   10.177%   $84.7812   $84.78   $84.80   $84.80  
  Purchase #2 $221.97   11.436%   $247.3545   $247.35   $247.35   $247.40  
  Purchase #3 $227.38   4.569%   $237.769   $237.77   $237.75   $237.80  
  Purchase #4 $215.84   6.788%   $230.4912   $230.49   $230.50   $230.50  
  Purchase #5 $202.42   7.490%   $217.5813   $217.58   $217.60   $217.60  
  Purchase #6 $141.26   12.605%   $159.0658   $159.07   $159.05   $159.10  
  Purchase #7 $52.88   11.239%   $58.8232   $58.82   $58.80   $58.80  
  7 purchase totals = $1,138.70       $1,235.8662   $1,235.86   $1,235.85   $1,236.00