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 $31.36   6.596%   $33.4285   $33.43   $33.45   $33.40  
  Purchase #2 $245.50   8.784%   $267.0647   $267.06   $267.05   $267.10  
  Purchase #3 $92.98   3.587%   $96.3152   $96.32   $96.30   $96.30  
  Purchase #4 $87.69   8.211%   $94.8902   $94.89   $94.90   $94.90  
  Purchase #5 $11.81   11.628%   $13.1833   $13.18   $13.20   $13.20  
  Purchase #6 $208.45   4.119%   $217.0361   $217.04   $217.05   $217.00  
  Purchase #7 $57.34   13.328%   $64.9823   $64.98   $65.00   $65.00  
  7 purchase totals = $735.13       $786.9003   $786.90   $786.95   $786.90