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 $62.30   6.312%   $66.2324   $66.23   $66.25   $66.20  
  Purchase #2 $84.41   13.241%   $95.5867   $95.59   $95.60   $95.60  
  Purchase #3 $98.37   6.426%   $104.6913   $104.69   $104.70   $104.70  
  Purchase #4 $161.54   4.828%   $169.3392   $169.34   $169.35   $169.30  
  Purchase #5 $96.99   7.717%   $104.4747   $104.47   $104.45   $104.50  
  Purchase #6 $95.98   5.279%   $101.0468   $101.05   $101.05   $101.00  
  Purchase #7 $5.45   7.524%   $5.8601   $5.86   $5.85   $5.90  
  7 purchase totals = $605.04       $647.2312   $647.23   $647.25   $647.20