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	$78.92	12.245%	$88.5838	$88.58	$88.60	$88.60
Purchase #2	$133.30	13.705%	$151.5688	$151.57	$151.55	$151.60
Purchase #3	$62.66	6.145%	$66.5105	$66.51	$66.50	$66.50
Purchase #4	$145.73	4.365%	$152.0911	$152.09	$152.10	$152.10
Purchase #5	$199.82	7.645%	$215.0962	$215.10	$215.10	$215.10
Purchase #6	$183.98	13.275%	$208.4033	$208.40	$208.40	$208.40
Purchase #7	$50.75	8.311%	$54.9678	$54.97	$54.95	$55.00
7 purchase totals =	$855.16		$937.2215	$937.22	$937.20	$937.30