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	$40.76	4.614%	$42.6407	$42.64	$42.65	$42.60
Purchase #2	$80.91	11.520%	$90.2308	$90.23	$90.25	$90.20
Purchase #3	$129.34	6.381%	$137.5932	$137.59	$137.60	$137.60
Purchase #4	$32.41	4.645%	$33.9154	$33.92	$33.90	$33.90
Purchase #5	$242.44	9.478%	$265.4185	$265.42	$265.40	$265.40
Purchase #6	$9.54	4.662%	$9.9848	$9.98	$10.00	$10.00
Purchase #7	$214.72	13.773%	$244.2934	$244.29	$244.30	$244.30
7 purchase totals =	$750.12		$824.0768	$824.07	$824.10	$824.00