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	$64.62	10.403%	$71.3424	$71.34	$71.35	$71.30
Purchase #2	$88.69	5.718%	$93.7613	$93.76	$93.75	$93.80
Purchase #3	$82.72	10.851%	$91.6959	$91.70	$91.70	$91.70
Purchase #4	$78.65	4.613%	$82.2781	$82.28	$82.30	$82.30
Purchase #5	$111.48	11.771%	$124.6023	$124.60	$124.60	$124.60
Purchase #6	$191.35	11.494%	$213.3438	$213.34	$213.35	$213.30
Purchase #7	$139.83	13.574%	$158.8105	$158.81	$158.80	$158.80
7 purchase totals =	$757.34		$835.8343	$835.83	$835.85	$835.80