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	$105.27	11.545%	$117.4234	$117.42	$117.40	$117.40
Purchase #2	$79.88	11.591%	$89.1389	$89.14	$89.15	$89.10
Purchase #3	$152.70	10.623%	$168.9213	$168.92	$168.90	$168.90
Purchase #4	$180.70	13.502%	$205.0981	$205.10	$205.10	$205.10
Purchase #5	$36.35	11.289%	$40.4536	$40.45	$40.45	$40.50
Purchase #6	$13.64	11.621%	$15.2251	$15.23	$15.25	$15.20
Purchase #7	$54.84	12.369%	$61.6232	$61.62	$61.60	$61.60
7 purchase totals =	$623.38		$697.8836	$697.88	$697.85	$697.80