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	$120.44	9.275%	$131.6108	$131.61	$131.60	$131.60
Purchase #2	$235.87	4.429%	$246.3167	$246.32	$246.30	$246.30
Purchase #3	$127.31	11.133%	$141.4834	$141.48	$141.50	$141.50
Purchase #4	$37.25	9.475%	$40.7794	$40.78	$40.80	$40.80
Purchase #5	$57.80	4.618%	$60.4692	$60.47	$60.45	$60.50
Purchase #6	$181.86	3.369%	$187.9869	$187.99	$188.00	$188.00
Purchase #7	$65.74	7.118%	$70.4194	$70.42	$70.40	$70.40
7 purchase totals =	$826.27		$879.0658	$879.07	$879.05	$879.10