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	$25.70	11.251%	$28.5915	$28.59	$28.60	$28.60
Purchase #2	$34.87	7.263%	$37.4026	$37.40	$37.40	$37.40
Purchase #3	$236.29	11.820%	$264.2195	$264.22	$264.20	$264.20
Purchase #4	$248.30	11.640%	$277.2021	$277.20	$277.20	$277.20
Purchase #5	$58.52	11.337%	$65.1544	$65.15	$65.15	$65.20
Purchase #6	$168.38	5.851%	$178.2319	$178.23	$178.25	$178.20
Purchase #7	$78.38	5.331%	$82.5584	$82.56	$82.55	$82.60
7 purchase totals =	$850.44		$933.3604	$933.35	$933.35	$933.40