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	$102.63	6.328%	$109.1244	$109.12	$109.10	$109.10
Purchase #2	$187.88	4.745%	$196.7949	$196.79	$196.80	$196.80
Purchase #3	$122.83	9.193%	$134.1218	$134.12	$134.10	$134.10
Purchase #4	$102.30	10.302%	$112.8389	$112.84	$112.85	$112.80
Purchase #5	$62.58	8.217%	$67.7222	$67.72	$67.70	$67.70
Purchase #6	$232.78	12.330%	$261.4818	$261.48	$261.50	$261.50
Purchase #7	$36.31	9.204%	$39.652	$39.65	$39.65	$39.70
7 purchase totals =	$847.31		$921.7360	$921.72	$921.70	$921.70