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	$97.26	7.429%	$104.4854	$104.49	$104.50	$104.50
Purchase #2	$69.82	11.601%	$77.9198	$77.92	$77.90	$77.90
Purchase #3	$80.25	12.306%	$90.1256	$90.13	$90.15	$90.10
Purchase #4	$115.61	9.210%	$126.2577	$126.26	$126.25	$126.30
Purchase #5	$154.50	3.479%	$159.8751	$159.88	$159.90	$159.90
Purchase #6	$75.43	3.598%	$78.144	$78.14	$78.15	$78.10
Purchase #7	$48.92	12.224%	$54.9	$54.90	$54.90	$54.90
7 purchase totals =	$641.79		$691.7076	$691.72	$691.75	$691.70