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 $64.96   13.159%   $73.5081   $73.51   $73.50   $73.50  
  Purchase #2 $12.33   8.258%   $13.3482   $13.35   $13.35   $13.30  
  Purchase #3 $112.90   11.821%   $126.2459   $126.25   $126.25   $126.20  
  Purchase #4 $96.82   7.426%   $104.0099   $104.01   $104.00   $104.00  
  Purchase #5 $52.96   13.448%   $60.0821   $60.08   $60.10   $60.10  
  Purchase #6 $187.29   8.859%   $203.882   $203.88   $203.90   $203.90  
  Purchase #7 $199.53   5.486%   $210.4762   $210.48   $210.50   $210.50  
  7 purchase totals = $726.79       $791.5524   $791.56   $791.60   $791.50