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 $197.76   10.779%   $219.0766   $219.08   $219.10   $219.10  
  Purchase #2 $136.99   12.382%   $153.9521   $153.95   $153.95   $154.00  
  Purchase #3 $57.79   11.259%   $64.2966   $64.30   $64.30   $64.30  
  Purchase #4 $159.75   8.537%   $173.3879   $173.39   $173.40   $173.40  
  Purchase #5 $41.53   8.203%   $44.9367   $44.94   $44.95   $44.90  
  Purchase #6 $48.98   11.537%   $54.6308   $54.63   $54.65   $54.60  
  Purchase #7 $228.35   9.703%   $250.5068   $250.51   $250.50   $250.50  
  7 purchase totals = $871.15       $960.7875   $960.80   $960.85   $960.80