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 $240.58   9.377%   $263.1392   $263.14   $263.15   $263.10  
  Purchase #2 $170.31   9.176%   $185.9376   $185.94   $185.95   $185.90  
  Purchase #3 $104.64   10.846%   $115.9893   $115.99   $116.00   $116.00  
  Purchase #4 $202.62   12.693%   $228.3386   $228.34   $228.35   $228.30  
  Purchase #5 $215.96   11.559%   $240.9228   $240.92   $240.90   $240.90  
  Purchase #6 $249.87   12.506%   $281.1187   $281.12   $281.10   $281.10  
  Purchase #7 $72.27   9.834%   $79.377   $79.38   $79.40   $79.40  
  7 purchase totals = $1,256.25       $1,394.8232   $1,394.83   $1,394.85   $1,394.70