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	$84.58	5.641%	$89.3512	$89.35	$89.35	$89.40
Purchase #2	$113.86	11.243%	$126.6613	$126.66	$126.65	$126.70
Purchase #3	$143.75	11.573%	$160.3862	$160.39	$160.40	$160.40
Purchase #4	$200.27	7.308%	$214.9057	$214.91	$214.90	$214.90
Purchase #5	$36.47	13.498%	$41.3927	$41.39	$41.40	$41.40
Purchase #6	$146.47	8.711%	$159.229	$159.23	$159.25	$159.20
Purchase #7	$137.64	11.718%	$153.7687	$153.77	$153.75	$153.80
7 purchase totals =	$863.04		$945.6948	$945.70	$945.70	$945.80