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	$190.99	12.826%	$215.4864	$215.49	$215.50	$215.50
Purchase #2	$194.31	11.279%	$216.2262	$216.23	$216.25	$216.20
Purchase #3	$74.73	10.254%	$82.3928	$82.39	$82.40	$82.40
Purchase #4	$136.66	5.276%	$143.8702	$143.87	$143.85	$143.90
Purchase #5	$11.44	4.292%	$11.931	$11.93	$11.95	$11.90
Purchase #6	$52.48	3.673%	$54.4076	$54.41	$54.40	$54.40
Purchase #7	$223.95	13.741%	$254.723	$254.72	$254.70	$254.70
7 purchase totals =	$884.56		$979.0372	$979.04	$979.05	$979.00