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 $116.82   4.203%   $121.7299   $121.73   $121.75   $121.70  
  Purchase #2 $87.28   4.665%   $91.3516   $91.35   $91.35   $91.40  
  Purchase #3 $78.97   13.615%   $89.7218   $89.72   $89.70   $89.70  
  Purchase #4 $14.93   3.533%   $15.4575   $15.46   $15.45   $15.50  
  Purchase #5 $221.33   12.113%   $248.1397   $248.14   $248.15   $248.10  
  Purchase #6 $236.72   13.377%   $268.386   $268.39   $268.40   $268.40  
  Purchase #7 $103.30   3.751%   $107.1748   $107.17   $107.15   $107.20  
  7 purchase totals = $859.35       $941.9613   $941.96   $941.95   $942.00