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 $217.48   6.799%   $232.2665   $232.27   $232.25   $232.30  
  Purchase #2 $156.81   8.820%   $170.6406   $170.64   $170.65   $170.60  
  Purchase #3 $222.97   13.486%   $253.0397   $253.04   $253.05   $253.00  
  Purchase #4 $199.25   5.606%   $210.42   $210.42   $210.40   $210.40  
  Purchase #5 $241.84   3.417%   $250.1037   $250.10   $250.10   $250.10  
  Purchase #6 $228.52   4.739%   $239.3496   $239.35   $239.35   $239.30  
  Purchase #7 $108.99   9.192%   $119.0084   $119.01   $119.00   $119.00  
  7 purchase totals = $1,375.86       $1,474.8285   $1,474.83   $1,474.80   $1,474.70