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 $95.97   3.771%   $99.589   $99.59   $99.60   $99.60  
  Purchase #2 $12.57   3.819%   $13.05   $13.05   $13.05   $13.10  
  Purchase #3 $44.76   5.844%   $47.3758   $47.38   $47.40   $47.40  
  Purchase #4 $71.99   4.114%   $74.9517   $74.95   $74.95   $75.00  
  Purchase #5 $196.91   5.600%   $207.937   $207.94   $207.95   $207.90  
  Purchase #6 $85.78   9.557%   $93.978   $93.98   $94.00   $94.00  
  Purchase #7 $34.37   9.143%   $37.5124   $37.51   $37.50   $37.50  
  7 purchase totals = $542.35       $574.3939   $574.40   $574.45   $574.50