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	$50.88	4.790%	$53.3172	$53.32	$53.30	$53.30
Purchase #2	$238.52	6.357%	$253.6827	$253.68	$253.70	$253.70
Purchase #3	$98.43	6.766%	$105.0898	$105.09	$105.10	$105.10
Purchase #4	$172.44	11.157%	$191.6791	$191.68	$191.70	$191.70
Purchase #5	$123.90	6.113%	$131.474	$131.47	$131.45	$131.50
Purchase #6	$81.88	11.643%	$91.4133	$91.41	$91.40	$91.40
Purchase #7	$69.95	10.629%	$77.385	$77.39	$77.40	$77.40
7 purchase totals =	$836.00		$904.0411	$904.04	$904.05	$904.10