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 $44.79   8.362%   $48.5353   $48.54   $48.55   $48.50  
  Purchase #2 $63.50   4.134%   $66.1251   $66.13   $66.15   $66.10  
  Purchase #3 $205.47   11.303%   $228.6943   $228.69   $228.70   $228.70  
  Purchase #4 $82.89   11.274%   $92.235   $92.24   $92.25   $92.20  
  Purchase #5 $71.34   8.244%   $77.2213   $77.22   $77.20   $77.20  
  Purchase #6 $228.85   3.461%   $236.7705   $236.77   $236.75   $236.80  
  Purchase #7 $119.65   9.697%   $131.2525   $131.25   $131.25   $131.30  
  7 purchase totals = $816.49       $880.8340   $880.84   $880.85   $880.80