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 $119.38   3.811%   $123.9296   $123.93   $123.95   $123.90  
  Purchase #2 $60.66   7.452%   $65.1804   $65.18   $65.20   $65.20  
  Purchase #3 $191.48   10.510%   $211.6045   $211.60   $211.60   $211.60  
  Purchase #4 $236.43   11.335%   $263.2293   $263.23   $263.25   $263.20  
  Purchase #5 $167.86   4.639%   $175.647   $175.65   $175.65   $175.60  
  Purchase #6 $19.57   10.288%   $21.5834   $21.58   $21.60   $21.60  
  Purchase #7 $135.28   10.242%   $149.1354   $149.14   $149.15   $149.10  
  7 purchase totals = $930.66       $1,010.3096   $1,010.31   $1,010.40   $1,010.20