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 $220.51   11.435%   $245.7253   $245.73   $245.75   $245.70  
  Purchase #2 $90.54   5.381%   $95.412   $95.41   $95.40   $95.40  
  Purchase #3 $52.99   9.382%   $57.9615   $57.96   $57.95   $58.00  
  Purchase #4 $46.45   3.191%   $47.9322   $47.93   $47.95   $47.90  
  Purchase #5 $24.49   12.213%   $27.481   $27.48   $27.50   $27.50  
  Purchase #6 $119.34   3.608%   $123.6458   $123.65   $123.65   $123.60  
  Purchase #7 $83.95   11.600%   $93.6882   $93.69   $93.70   $93.70  
  7 purchase totals = $638.27       $691.8460   $691.85   $691.90   $691.80