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	$79.94	13.488%	$90.7223	$90.72	$90.70	$90.70
Purchase #2	$169.39	9.742%	$185.892	$185.89	$185.90	$185.90
Purchase #3	$22.81	6.335%	$24.255	$24.26	$24.25	$24.30
Purchase #4	$149.39	6.340%	$158.8613	$158.86	$158.85	$158.90
Purchase #5	$171.63	10.753%	$190.0854	$190.09	$190.10	$190.10
Purchase #6	$211.85	5.468%	$223.434	$223.43	$223.45	$223.40
Purchase #7	$202.67	7.113%	$217.0859	$217.09	$217.10	$217.10
7 purchase totals =	$1,007.68		$1,090.3359	$1,090.34	$1,090.35	$1,090.40