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	$47.80	6.275%	$50.7995	$50.80	$50.80	$50.80
Purchase #2	$185.73	13.143%	$210.1405	$210.14	$210.15	$210.10
Purchase #3	$64.75	4.337%	$67.5582	$67.56	$67.55	$67.60
Purchase #4	$145.38	13.591%	$165.1386	$165.14	$165.15	$165.10
Purchase #5	$29.62	8.547%	$32.1516	$32.15	$32.15	$32.20
Purchase #6	$74.72	9.154%	$81.5599	$81.56	$81.55	$81.60
Purchase #7	$78.79	5.493%	$83.1179	$83.12	$83.10	$83.10
7 purchase totals =	$626.79		$690.4662	$690.47	$690.45	$690.50