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 $124.88   13.441%   $141.6651   $141.67   $141.65   $141.70  
  Purchase #2 $131.36   6.537%   $139.947   $139.95   $139.95   $139.90  
  Purchase #3 $125.64   8.115%   $135.8357   $135.84   $135.85   $135.80  
  Purchase #4 $228.97   13.320%   $259.4688   $259.47   $259.45   $259.50  
  Purchase #5 $187.62   4.289%   $195.667   $195.67   $195.65   $195.70  
  Purchase #6 $233.58   9.842%   $256.5689   $256.57   $256.55   $256.60  
  Purchase #7 $176.28   10.727%   $195.1896   $195.19   $195.20   $195.20  
  7 purchase totals = $1,208.33       $1,324.3421   $1,324.36   $1,324.30   $1,324.40