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 $67.33   13.510%   $76.4263   $76.43   $76.45   $76.40  
  Purchase #2 $240.80   10.561%   $266.2309   $266.23   $266.25   $266.20  
  Purchase #3 $173.28   10.258%   $191.0551   $191.06   $191.05   $191.10  
  Purchase #4 $62.84   6.499%   $66.924   $66.92   $66.90   $66.90  
  Purchase #5 $83.46   10.622%   $92.3251   $92.33   $92.35   $92.30  
  Purchase #6 $195.56   10.553%   $216.1974   $216.20   $216.20   $216.20  
  Purchase #7 $231.46   4.637%   $242.1928   $242.19   $242.20   $242.20  
  7 purchase totals = $1,054.73       $1,151.3516   $1,151.36   $1,151.40   $1,151.30