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	$46.45	3.427%	$48.0418	$48.04	$48.05	$48.00
Purchase #2	$183.76	6.459%	$195.6291	$195.63	$195.65	$195.60
Purchase #3	$122.78	12.170%	$137.7223	$137.72	$137.70	$137.70
Purchase #4	$26.59	3.223%	$27.447	$27.45	$27.45	$27.40
Purchase #5	$244.66	4.402%	$255.4299	$255.43	$255.45	$255.40
Purchase #6	$147.54	12.425%	$165.8718	$165.87	$165.85	$165.90
Purchase #7	$245.83	13.318%	$278.5696	$278.57	$278.55	$278.60
7 purchase totals =	$1,017.61		$1,108.7115	$1,108.71	$1,108.70	$1,108.60