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 $97.57   11.638%   $108.9252   $108.93   $108.95   $108.90  
  Purchase #2 $50.82   9.706%   $55.7526   $55.75   $55.75   $55.80  
  Purchase #3 $84.39   10.874%   $93.5666   $93.57   $93.55   $93.60  
  Purchase #4 $71.98   5.452%   $75.9043   $75.90   $75.90   $75.90  
  Purchase #5 $205.69   6.305%   $218.6588   $218.66   $218.65   $218.70  
  Purchase #6 $44.30   7.484%   $47.6154   $47.62   $47.60   $47.60  
  Purchase #7 $148.56   7.549%   $159.7748   $159.77   $159.75   $159.80  
  7 purchase totals = $703.31       $760.1977   $760.20   $760.15   $760.30