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	$141.77	6.824%	$151.4444	$151.44	$151.45	$151.40
Purchase #2	$248.66	4.794%	$260.5808	$260.58	$260.60	$260.60
Purchase #3	$92.63	13.407%	$105.0489	$105.05	$105.05	$105.00
Purchase #4	$64.82	12.447%	$72.8881	$72.89	$72.90	$72.90
Purchase #5	$123.42	11.474%	$137.5812	$137.58	$137.60	$137.60
Purchase #6	$71.68	9.638%	$78.5885	$78.59	$78.60	$78.60
Purchase #7	$22.48	7.370%	$24.1368	$24.14	$24.15	$24.10
7 purchase totals =	$765.46		$830.2687	$830.27	$830.35	$830.20