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	$103.89	12.774%	$117.1609	$117.16	$117.15	$117.20
Purchase #2	$94.63	6.713%	$100.9825	$100.98	$101.00	$101.00
Purchase #3	$171.92	4.197%	$179.1355	$179.14	$179.15	$179.10
Purchase #4	$133.60	12.811%	$150.7155	$150.72	$150.70	$150.70
Purchase #5	$238.34	13.458%	$270.4158	$270.42	$270.40	$270.40
Purchase #6	$73.65	3.731%	$76.3979	$76.40	$76.40	$76.40
Purchase #7	$199.45	12.114%	$223.6114	$223.61	$223.60	$223.60
7 purchase totals =	$1,015.48		$1,118.4195	$1,118.43	$1,118.40	$1,118.40