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	$205.51	12.831%	$231.879	$231.88	$231.90	$231.90
Purchase #2	$187.84	6.294%	$199.6626	$199.66	$199.65	$199.70
Purchase #3	$32.51	11.711%	$36.3172	$36.32	$36.30	$36.30
Purchase #4	$138.95	5.634%	$146.7784	$146.78	$146.80	$146.80
Purchase #5	$129.61	9.324%	$141.6948	$141.69	$141.70	$141.70
Purchase #6	$158.56	4.840%	$166.2343	$166.23	$166.25	$166.20
Purchase #7	$184.71	6.431%	$196.5887	$196.59	$196.60	$196.60
7 purchase totals =	$1,037.69		$1,119.1550	$1,119.15	$1,119.20	$1,119.20