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 $113.32   12.411%   $127.3841   $127.38   $127.40   $127.40  
  Purchase #2 $151.83   9.461%   $166.1946   $166.19   $166.20   $166.20  
  Purchase #3 $112.86   4.403%   $117.8292   $117.83   $117.85   $117.80  
  Purchase #4 $250.76   6.473%   $266.9917   $266.99   $267.00   $267.00  
  Purchase #5 $195.84   3.652%   $202.9921   $202.99   $203.00   $203.00  
  Purchase #6 $19.63   11.480%   $21.8835   $21.88   $21.90   $21.90  
  Purchase #7 $116.39   11.111%   $129.3221   $129.32   $129.30   $129.30  
  7 purchase totals = $960.63       $1,032.5973   $1,032.58   $1,032.65   $1,032.60