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	$63.35	10.689%	$70.1215	$70.12	$70.10	$70.10
Purchase #2	$222.77	7.762%	$240.0614	$240.06	$240.05	$240.10
Purchase #3	$136.52	6.701%	$145.6682	$145.67	$145.65	$145.70
Purchase #4	$203.72	12.110%	$228.3905	$228.39	$228.40	$228.40
Purchase #5	$115.74	13.847%	$131.7665	$131.77	$131.75	$131.80
Purchase #6	$121.81	7.132%	$130.4975	$130.50	$130.50	$130.50
Purchase #7	$50.57	4.801%	$52.9979	$53.00	$53.00	$53.00
7 purchase totals =	$914.48		$999.5035	$999.51	$999.45	$999.60