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 $216.83   6.607%   $231.156   $231.16   $231.15   $231.20  
  Purchase #2 $144.54   8.388%   $156.664   $156.66   $156.65   $156.70  
  Purchase #3 $23.71   9.735%   $26.0182   $26.02   $26.00   $26.00  
  Purchase #4 $117.27   9.525%   $128.44   $128.44   $128.45   $128.40  
  Purchase #5 $103.41   10.362%   $114.1253   $114.13   $114.15   $114.10  
  Purchase #6 $59.95   8.264%   $64.9043   $64.90   $64.90   $64.90  
  Purchase #7 $219.38   11.826%   $245.3239   $245.32   $245.30   $245.30  
  7 purchase totals = $885.09       $966.6317   $966.63   $966.60   $966.60