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	$40.91	13.390%	$46.3878	$46.39	$46.40	$46.40
Purchase #2	$148.66	9.263%	$162.4304	$162.43	$162.45	$162.40
Purchase #3	$76.33	13.349%	$86.5193	$86.52	$86.50	$86.50
Purchase #4	$142.35	6.868%	$152.1266	$152.13	$152.15	$152.10
Purchase #5	$73.35	4.181%	$76.4168	$76.42	$76.40	$76.40
Purchase #6	$75.60	8.865%	$82.3019	$82.30	$82.30	$82.30
Purchase #7	$23.47	13.854%	$26.7215	$26.72	$26.70	$26.70
7 purchase totals =	$580.67		$632.9043	$632.91	$632.90	$632.80