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 $91.29   10.212%   $100.6125   $100.61   $100.60   $100.60  
  Purchase #2 $131.46   3.230%   $135.7062   $135.71   $135.70   $135.70  
  Purchase #3 $95.44   7.522%   $102.619   $102.62   $102.60   $102.60  
  Purchase #4 $249.72   4.274%   $260.393   $260.39   $260.40   $260.40  
  Purchase #5 $30.91   8.382%   $33.5009   $33.50   $33.50   $33.50  
  Purchase #6 $22.63   10.273%   $24.9548   $24.95   $24.95   $25.00  
  Purchase #7 $197.45   9.280%   $215.7734   $215.77   $215.75   $215.80  
  7 purchase totals = $818.90       $873.5598   $873.55   $873.50   $873.60