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	$29.38	13.674%	$33.3974	$33.40	$33.40	$33.40
Purchase #2	$155.71	7.517%	$167.4147	$167.41	$167.40	$167.40
Purchase #3	$144.38	11.362%	$160.7845	$160.78	$160.80	$160.80
Purchase #4	$159.75	7.284%	$171.3862	$171.39	$171.40	$171.40
Purchase #5	$195.31	13.650%	$221.9698	$221.97	$221.95	$222.00
Purchase #6	$89.28	12.793%	$100.7016	$100.70	$100.70	$100.70
Purchase #7	$122.51	6.772%	$130.8064	$130.81	$130.80	$130.80
7 purchase totals =	$896.32		$986.4606	$986.46	$986.45	$986.50