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	$59.30	8.342%	$64.2468	$64.25	$64.25	$64.20
Purchase #2	$122.28	12.116%	$137.0954	$137.10	$137.10	$137.10
Purchase #3	$64.50	12.822%	$72.7702	$72.77	$72.75	$72.80
Purchase #4	$123.62	5.281%	$130.1484	$130.15	$130.15	$130.10
Purchase #5	$76.88	4.514%	$80.3504	$80.35	$80.35	$80.40
Purchase #6	$182.49	7.774%	$196.6768	$196.68	$196.70	$196.70
Purchase #7	$154.51	9.444%	$169.1019	$169.10	$169.10	$169.10
7 purchase totals =	$783.58		$850.3899	$850.40	$850.40	$850.40