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 $72.45   3.562%   $75.0307   $75.03   $75.05   $75.00  
  Purchase #2 $202.43   12.277%   $227.2823   $227.28   $227.30   $227.30  
  Purchase #3 $175.90   12.716%   $198.2674   $198.27   $198.25   $198.30  
  Purchase #4 $39.40   13.207%   $44.6036   $44.60   $44.60   $44.60  
  Purchase #5 $208.42   6.465%   $221.8944   $221.89   $221.90   $221.90  
  Purchase #6 $30.40   5.297%   $32.0103   $32.01   $32.00   $32.00  
  Purchase #7 $34.38   9.837%   $37.762   $37.76   $37.75   $37.80  
  7 purchase totals = $763.38       $836.8507   $836.84   $836.85   $836.90