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	$70.88	11.356%	$78.9291	$78.93	$78.95	$78.90
Purchase #2	$247.87	6.129%	$263.062	$263.06	$263.05	$263.10
Purchase #3	$235.73	3.833%	$244.7655	$244.77	$244.75	$244.80
Purchase #4	$82.86	4.407%	$86.5116	$86.51	$86.50	$86.50
Purchase #5	$11.71	8.717%	$12.7308	$12.73	$12.75	$12.70
Purchase #6	$77.75	6.296%	$82.6451	$82.65	$82.65	$82.60
Purchase #7	$90.84	11.648%	$101.421	$101.42	$101.40	$101.40
7 purchase totals =	$817.64		$870.0651	$870.07	$870.05	$870.00