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 $237.26   3.812%   $246.3044   $246.30   $246.30   $246.30  
  Purchase #2 $178.69   9.186%   $195.1045   $195.10   $195.10   $195.10  
  Purchase #3 $49.25   12.301%   $55.3082   $55.31   $55.30   $55.30  
  Purchase #4 $152.32   12.452%   $171.2869   $171.29   $171.30   $171.30  
  Purchase #5 $249.93   3.672%   $259.1074   $259.11   $259.10   $259.10  
  Purchase #6 $247.45   7.537%   $266.1003   $266.10   $266.10   $266.10  
  Purchase #7 $196.56   10.869%   $217.9241   $217.92   $217.90   $217.90  
  7 purchase totals = $1,311.46       $1,411.1358   $1,411.13   $1,411.10   $1,411.10