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 $68.34   11.258%   $76.0337   $76.03   $76.05   $76.00  
  Purchase #2 $118.86   8.506%   $128.9702   $128.97   $128.95   $129.00  
  Purchase #3 $164.66   4.838%   $172.6263   $172.63   $172.65   $172.60  
  Purchase #4 $94.51   7.763%   $101.8468   $101.85   $101.85   $101.80  
  Purchase #5 $196.93   8.197%   $213.0724   $213.07   $213.05   $213.10  
  Purchase #6 $203.97   8.393%   $221.0892   $221.09   $221.10   $221.10  
  Purchase #7 $54.92   6.393%   $58.431   $58.43   $58.45   $58.40  
  7 purchase totals = $902.19       $972.0696   $972.07   $972.10   $972.00