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	$10.47	6.479%	$11.1484	$11.15	$11.15	$11.10
Purchase #2	$115.58	9.570%	$126.641	$126.64	$126.65	$126.60
Purchase #3	$131.84	13.702%	$149.9047	$149.90	$149.90	$149.90
Purchase #4	$74.64	3.273%	$77.083	$77.08	$77.10	$77.10
Purchase #5	$125.92	13.353%	$142.7341	$142.73	$142.75	$142.70
Purchase #6	$104.89	12.425%	$117.9226	$117.92	$117.90	$117.90
Purchase #7	$37.70	12.441%	$42.3903	$42.39	$42.40	$42.40
7 purchase totals =	$601.04		$667.8241	$667.81	$667.85	$667.70