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	$196.90	6.861%	$210.4093	$210.41	$210.40	$210.40
Purchase #2	$144.76	7.537%	$155.6706	$155.67	$155.65	$155.70
Purchase #3	$18.29	3.394%	$18.9108	$18.91	$18.90	$18.90
Purchase #4	$132.34	8.320%	$143.3507	$143.35	$143.35	$143.40
Purchase #5	$146.39	3.331%	$151.2663	$151.27	$151.25	$151.30
Purchase #6	$184.25	3.826%	$191.2994	$191.30	$191.30	$191.30
Purchase #7	$99.88	8.204%	$108.0742	$108.07	$108.05	$108.10
7 purchase totals =	$922.81		$978.9813	$978.98	$978.90	$979.10