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	$159.87	7.768%	$172.2887	$172.29	$172.30	$172.30
Purchase #2	$130.55	11.500%	$145.5633	$145.56	$145.55	$145.60
Purchase #3	$109.84	4.802%	$115.1145	$115.11	$115.10	$115.10
Purchase #4	$124.70	10.150%	$137.3571	$137.36	$137.35	$137.40
Purchase #5	$182.70	7.738%	$196.8373	$196.84	$196.85	$196.80
Purchase #6	$170.49	3.381%	$176.2543	$176.25	$176.25	$176.30
Purchase #7	$161.60	11.572%	$180.3004	$180.30	$180.30	$180.30
7 purchase totals =	$1,039.75		$1,123.7156	$1,123.71	$1,123.70	$1,123.80