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 $32.88   12.618%   $37.0288   $37.03   $37.05   $37.00  
  Purchase #2 $163.53   4.328%   $170.6076   $170.61   $170.60   $170.60  
  Purchase #3 $115.63   9.392%   $126.49   $126.49   $126.50   $126.50  
  Purchase #4 $250.39   8.496%   $271.6631   $271.66   $271.65   $271.70  
  Purchase #5 $47.76   10.534%   $52.791   $52.79   $52.80   $52.80  
  Purchase #6 $188.90   3.226%   $194.9939   $194.99   $195.00   $195.00  
  Purchase #7 $154.92   5.352%   $163.2113   $163.21   $163.20   $163.20  
  7 purchase totals = $954.01       $1,016.7857   $1,016.78   $1,016.80   $1,016.80