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	$123.27	6.597%	$131.4021	$131.40	$131.40	$131.40
Purchase #2	$152.62	4.343%	$159.2483	$159.25	$159.25	$159.20
Purchase #3	$228.84	11.811%	$255.8683	$255.87	$255.85	$255.90
Purchase #4	$125.33	12.846%	$141.4299	$141.43	$141.45	$141.40
Purchase #5	$210.58	3.265%	$217.4554	$217.46	$217.45	$217.50
Purchase #6	$208.75	5.713%	$220.6759	$220.68	$220.70	$220.70
Purchase #7	$248.63	10.624%	$275.0445	$275.04	$275.05	$275.00
7 purchase totals =	$1,298.02		$1,401.1244	$1,401.13	$1,401.15	$1,401.10