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	$123.42	9.319%	$134.9215	$134.92	$134.90	$134.90
Purchase #2	$240.78	6.551%	$256.5535	$256.55	$256.55	$256.60
Purchase #3	$62.80	6.417%	$66.8299	$66.83	$66.85	$66.80
Purchase #4	$152.82	9.557%	$167.425	$167.43	$167.45	$167.40
Purchase #5	$140.84	6.168%	$149.527	$149.53	$149.55	$149.50
Purchase #6	$132.64	7.267%	$142.2789	$142.28	$142.30	$142.30
Purchase #7	$34.51	11.513%	$38.4831	$38.48	$38.50	$38.50
7 purchase totals =	$887.81		$956.0189	$956.02	$956.10	$956.00