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 $21.42   4.585%   $22.4021   $22.40   $22.40   $22.40  
  Purchase #2 $24.77   9.498%   $27.1227   $27.12   $27.10   $27.10  
  Purchase #3 $129.41   13.476%   $146.8493   $146.85   $146.85   $146.80  
  Purchase #4 $79.95   3.359%   $82.6355   $82.64   $82.65   $82.60  
  Purchase #5 $235.35   8.431%   $255.1924   $255.19   $255.20   $255.20  
  Purchase #6 $201.72   11.731%   $225.3838   $225.38   $225.40   $225.40  
  Purchase #7 $81.63   6.744%   $87.1351   $87.14   $87.15   $87.10  
  7 purchase totals = $774.25       $846.7209   $846.72   $846.75   $846.60