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 $60.74   4.762%   $63.6324   $63.63   $63.65   $63.60  
  Purchase #2 $40.95   9.839%   $44.9791   $44.98   $45.00   $45.00  
  Purchase #3 $112.41   4.718%   $117.7135   $117.71   $117.70   $117.70  
  Purchase #4 $22.63   12.576%   $25.4759   $25.48   $25.50   $25.50  
  Purchase #5 $183.67   6.319%   $195.2761   $195.28   $195.30   $195.30  
  Purchase #6 $230.77   6.534%   $245.8485   $245.85   $245.85   $245.80  
  Purchase #7 $229.77   5.422%   $242.2281   $242.23   $242.25   $242.20  
  7 purchase totals = $880.94       $935.1536   $935.16   $935.25   $935.10