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 $18.26   7.726%   $19.6708   $19.67   $19.65   $19.70  
  Purchase #2 $72.70   7.416%   $78.0914   $78.09   $78.10   $78.10  
  Purchase #3 $124.64   6.517%   $132.7628   $132.76   $132.75   $132.80  
  Purchase #4 $100.33   12.640%   $113.0117   $113.01   $113.00   $113.00  
  Purchase #5 $215.40   12.808%   $242.9884   $242.99   $243.00   $243.00  
  Purchase #6 $7.74   4.571%   $8.0938   $8.09   $8.10   $8.10  
  Purchase #7 $198.28   9.297%   $216.7141   $216.71   $216.70   $216.70  
  7 purchase totals = $737.35       $811.3330   $811.32   $811.30   $811.40