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	$201.35	10.593%	$222.679	$222.68	$222.70	$222.70
Purchase #2	$54.64	4.289%	$56.9835	$56.98	$57.00	$57.00
Purchase #3	$42.86	8.479%	$46.4941	$46.49	$46.50	$46.50
Purchase #4	$82.78	6.672%	$88.3031	$88.30	$88.30	$88.30
Purchase #5	$87.91	13.639%	$99.9	$99.90	$99.90	$99.90
Purchase #6	$60.42	6.388%	$64.2796	$64.28	$64.30	$64.30
Purchase #7	$102.75	7.517%	$110.4737	$110.47	$110.45	$110.50
7 purchase totals =	$632.71		$689.1130	$689.10	$689.15	$689.20