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 $60.95   11.758%   $68.1165   $68.12   $68.10   $68.10  
  Purchase #2 $47.29   11.248%   $52.6092   $52.61   $52.60   $52.60  
  Purchase #3 $194.73   6.404%   $207.2005   $207.20   $207.20   $207.20  
  Purchase #4 $146.54   11.718%   $163.7116   $163.71   $163.70   $163.70  
  Purchase #5 $178.65   9.610%   $195.8183   $195.82   $195.80   $195.80  
  Purchase #6 $231.56   10.428%   $255.7071   $255.71   $255.70   $255.70  
  Purchase #7 $70.60   4.202%   $73.5666   $73.57   $73.55   $73.60  
  7 purchase totals = $930.32       $1,016.7298   $1,016.74   $1,016.65   $1,016.70