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	$84.41	9.139%	$92.1242	$92.12	$92.10	$92.10
Purchase #2	$175.90	7.276%	$188.6985	$188.70	$188.70	$188.70
Purchase #3	$74.40	4.187%	$77.5151	$77.52	$77.50	$77.50
Purchase #4	$105.81	12.408%	$118.9389	$118.94	$118.95	$118.90
Purchase #5	$62.40	8.838%	$67.9149	$67.91	$67.90	$67.90
Purchase #6	$138.51	9.496%	$151.6629	$151.66	$151.65	$151.70
Purchase #7	$130.45	5.400%	$137.4943	$137.49	$137.50	$137.50
7 purchase totals =	$771.88		$834.3488	$834.34	$834.30	$834.30