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 $117.64   3.402%   $121.6421   $121.64   $121.65   $121.60  
  Purchase #2 $195.43   4.134%   $203.5091   $203.51   $203.50   $203.50  
  Purchase #3 $120.47   5.551%   $127.1573   $127.16   $127.15   $127.20  
  Purchase #4 $173.44   8.633%   $188.4131   $188.41   $188.40   $188.40  
  Purchase #5 $22.48   11.398%   $25.0423   $25.04   $25.05   $25.00  
  Purchase #6 $193.41   11.223%   $215.1164   $215.12   $215.10   $215.10  
  Purchase #7 $29.79   8.231%   $32.242   $32.24   $32.25   $32.20  
  7 purchase totals = $852.66       $913.1223   $913.12   $913.10   $913.00