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 $59.93   9.779%   $65.7906   $65.79   $65.80   $65.80  
  Purchase #2 $140.76   5.596%   $148.6369   $148.64   $148.65   $148.60  
  Purchase #3 $86.64   10.499%   $95.7363   $95.74   $95.75   $95.70  
  Purchase #4 $208.70   4.177%   $217.4174   $217.42   $217.40   $217.40  
  Purchase #5 $103.73   3.226%   $107.0763   $107.08   $107.10   $107.10  
  Purchase #6 $203.75   3.543%   $210.9689   $210.97   $210.95   $211.00  
  Purchase #7 $96.94   4.182%   $100.994   $100.99   $101.00   $101.00  
  7 purchase totals = $900.45       $946.6204   $946.63   $946.65   $946.60