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	$10.72	12.531%	$12.0633	$12.06	$12.05	$12.10
Purchase #2	$157.63	11.280%	$175.4107	$175.41	$175.40	$175.40
Purchase #3	$79.80	10.672%	$88.3163	$88.32	$88.30	$88.30
Purchase #4	$129.78	11.158%	$144.2609	$144.26	$144.25	$144.30
Purchase #5	$24.51	11.683%	$27.3735	$27.37	$27.35	$27.40
Purchase #6	$160.80	12.832%	$181.4339	$181.43	$181.45	$181.40
Purchase #7	$137.36	6.185%	$145.8557	$145.86	$145.85	$145.90
7 purchase totals =	$700.60		$774.7143	$774.71	$774.65	$774.80