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 $41.35   8.304%   $44.7837   $44.78   $44.80   $44.80  
  Purchase #2 $164.54   11.349%   $183.2136   $183.21   $183.20   $183.20  
  Purchase #3 $131.75   9.485%   $144.2465   $144.25   $144.25   $144.20  
  Purchase #4 $25.74   13.862%   $29.3081   $29.31   $29.30   $29.30  
  Purchase #5 $102.30   6.216%   $108.659   $108.66   $108.65   $108.70  
  Purchase #6 $121.66   12.207%   $136.511   $136.51   $136.50   $136.50  
  Purchase #7 $107.25   11.685%   $119.7822   $119.78   $119.80   $119.80  
  7 purchase totals = $694.59       $766.5041   $766.50   $766.50   $766.50