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	$133.46	4.247%	$139.128	$139.13	$139.15	$139.10
Purchase #2	$93.35	6.834%	$99.7295	$99.73	$99.75	$99.70
Purchase #3	$44.39	7.600%	$47.7636	$47.76	$47.75	$47.80
Purchase #4	$226.32	3.329%	$233.8542	$233.85	$233.85	$233.90
Purchase #5	$237.95	5.244%	$250.4281	$250.43	$250.45	$250.40
Purchase #6	$137.80	11.134%	$153.1427	$153.14	$153.15	$153.10
Purchase #7	$64.54	7.690%	$69.5031	$69.50	$69.50	$69.50
7 purchase totals =	$937.81		$993.5492	$993.54	$993.60	$993.50