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	$76.43	5.670%	$80.7636	$80.76	$80.75	$80.80
Purchase #2	$34.60	7.297%	$37.1248	$37.12	$37.10	$37.10
Purchase #3	$10.34	5.839%	$10.9438	$10.94	$10.95	$10.90
Purchase #4	$199.90	5.105%	$210.1049	$210.10	$210.10	$210.10
Purchase #5	$226.49	6.103%	$240.3127	$240.31	$240.30	$240.30
Purchase #6	$144.81	3.802%	$150.3157	$150.32	$150.30	$150.30
Purchase #7	$215.41	11.665%	$240.5376	$240.54	$240.55	$240.50
7 purchase totals =	$907.98		$970.1031	$970.09	$970.05	$970.00