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	$19.40	6.315%	$20.6251	$20.63	$20.65	$20.60
Purchase #2	$60.72	8.322%	$65.7731	$65.77	$65.75	$65.80
Purchase #3	$104.43	9.740%	$114.6015	$114.60	$114.60	$114.60
Purchase #4	$73.65	13.657%	$83.7084	$83.71	$83.70	$83.70
Purchase #5	$9.56	13.620%	$10.8621	$10.86	$10.85	$10.90
Purchase #6	$148.54	10.781%	$164.5541	$164.55	$164.55	$164.60
Purchase #7	$99.52	6.140%	$105.6305	$105.63	$105.65	$105.60
7 purchase totals =	$515.82		$565.7548	$565.75	$565.75	$565.80