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 $64.41   6.343%   $68.4955   $68.50   $68.50   $68.50  
  Purchase #2 $176.50   8.385%   $191.2995   $191.30   $191.30   $191.30  
  Purchase #3 $42.42   8.578%   $46.0588   $46.06   $46.05   $46.10  
  Purchase #4 $248.69   10.457%   $274.6955   $274.70   $274.70   $274.70  
  Purchase #5 $245.74   3.405%   $254.1074   $254.11   $254.10   $254.10  
  Purchase #6 $229.51   4.783%   $240.4875   $240.49   $240.50   $240.50  
  Purchase #7 $119.96   3.488%   $124.1442   $124.14   $124.15   $124.10  
  7 purchase totals = $1,127.23       $1,199.2884   $1,199.30   $1,199.30   $1,199.30