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 $85.60   12.707%   $96.4772   $96.48   $96.50   $96.50  
  Purchase #2 $61.53   8.845%   $66.9723   $66.97   $66.95   $67.00  
  Purchase #3 $48.72   11.715%   $54.4275   $54.43   $54.45   $54.40  
  Purchase #4 $250.74   10.648%   $277.4388   $277.44   $277.45   $277.40  
  Purchase #5 $84.73   9.728%   $92.9725   $92.97   $92.95   $93.00  
  Purchase #6 $30.82   11.736%   $34.437   $34.44   $34.45   $34.40  
  Purchase #7 $108.57   11.350%   $120.8927   $120.89   $120.90   $120.90  
  7 purchase totals = $670.71       $743.6180   $743.62   $743.65   $743.60