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	$30.77	4.160%	$32.05	$32.05	$32.05	$32.10
Purchase #2	$139.52	9.153%	$152.2903	$152.29	$152.30	$152.30
Purchase #3	$95.66	13.749%	$108.8123	$108.81	$108.80	$108.80
Purchase #4	$205.28	11.847%	$229.5995	$229.60	$229.60	$229.60
Purchase #5	$139.27	6.412%	$148.2	$148.20	$148.20	$148.20
Purchase #6	$75.82	13.380%	$85.9647	$85.96	$85.95	$86.00
Purchase #7	$120.29	9.226%	$131.388	$131.39	$131.40	$131.40
7 purchase totals =	$806.61		$888.3048	$888.30	$888.30	$888.40