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 $241.57   5.819%   $255.627   $255.63   $255.65   $255.60  
  Purchase #2 $15.43   9.106%   $16.8351   $16.84   $16.85   $16.80  
  Purchase #3 $249.66   10.543%   $275.9817   $275.98   $276.00   $276.00  
  Purchase #4 $190.33   11.188%   $211.6241   $211.62   $211.60   $211.60  
  Purchase #5 $72.68   12.756%   $81.9511   $81.95   $81.95   $82.00  
  Purchase #6 $178.46   4.369%   $186.2569   $186.26   $186.25   $186.30  
  Purchase #7 $113.27   5.237%   $119.2019   $119.20   $119.20   $119.20  
  7 purchase totals = $1,061.40       $1,147.4778   $1,147.48   $1,147.50   $1,147.50