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 $203.50   4.140%   $211.9249   $211.92   $211.90   $211.90  
  Purchase #2 $116.54   7.154%   $124.8773   $124.88   $124.90   $124.90  
  Purchase #3 $15.45   5.502%   $16.3001   $16.30   $16.30   $16.30  
  Purchase #4 $190.38   11.797%   $212.8391   $212.84   $212.85   $212.80  
  Purchase #5 $215.70   9.693%   $236.6078   $236.61   $236.60   $236.60  
  Purchase #6 $147.26   11.187%   $163.734   $163.73   $163.75   $163.70  
  Purchase #7 $161.96   8.662%   $175.989   $175.99   $176.00   $176.00  
  7 purchase totals = $1,050.79       $1,142.2722   $1,142.27   $1,142.30   $1,142.20