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	$136.89	3.117%	$141.1569	$141.16	$141.15	$141.20
Purchase #2	$83.46	9.724%	$91.5757	$91.58	$91.60	$91.60
Purchase #3	$60.68	6.729%	$64.7632	$64.76	$64.75	$64.80
Purchase #4	$235.27	12.133%	$263.8153	$263.82	$263.80	$263.80
Purchase #5	$97.93	7.662%	$105.4334	$105.43	$105.45	$105.40
Purchase #6	$89.32	8.697%	$97.0882	$97.09	$97.10	$97.10
Purchase #7	$196.77	9.856%	$216.1637	$216.16	$216.15	$216.20
7 purchase totals =	$900.32		$979.9964	$980.00	$980.00	$980.10