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	$26.41	6.453%	$28.1142	$28.11	$28.10	$28.10
Purchase #2	$79.62	3.447%	$82.3645	$82.36	$82.35	$82.40
Purchase #3	$69.64	12.521%	$78.3596	$78.36	$78.35	$78.40
Purchase #4	$121.32	7.524%	$130.4481	$130.45	$130.45	$130.40
Purchase #5	$228.80	10.292%	$252.3481	$252.35	$252.35	$252.30
Purchase #6	$72.69	7.580%	$78.1999	$78.20	$78.20	$78.20
Purchase #7	$28.67	4.241%	$29.8859	$29.89	$29.90	$29.90
7 purchase totals =	$627.15		$679.7203	$679.72	$679.70	$679.70