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	$16.49	7.454%	$17.7192	$17.72	$17.70	$17.70
Purchase #2	$221.47	4.383%	$231.177	$231.18	$231.20	$231.20
Purchase #3	$123.34	3.589%	$127.7667	$127.77	$127.75	$127.80
Purchase #4	$36.31	7.131%	$38.8993	$38.90	$38.90	$38.90
Purchase #5	$186.70	5.191%	$196.3916	$196.39	$196.40	$196.40
Purchase #6	$237.30	9.147%	$259.0058	$259.01	$259.00	$259.00
Purchase #7	$232.98	8.370%	$252.4804	$252.48	$252.50	$252.50
7 purchase totals =	$1,054.59		$1,123.4400	$1,123.45	$1,123.45	$1,123.50