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	$152.90	4.834%	$160.2912	$160.29	$160.30	$160.30
Purchase #2	$28.31	3.453%	$29.2875	$29.29	$29.30	$29.30
Purchase #3	$65.64	10.334%	$72.4232	$72.42	$72.40	$72.40
Purchase #4	$37.61	8.860%	$40.9422	$40.94	$40.95	$40.90
Purchase #5	$229.66	10.422%	$253.5952	$253.60	$253.60	$253.60
Purchase #6	$191.69	12.461%	$215.5765	$215.58	$215.60	$215.60
Purchase #7	$28.33	8.820%	$30.8287	$30.83	$30.85	$30.80
7 purchase totals =	$734.14		$802.9445	$802.95	$803.00	$802.90