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	$223.85	12.301%	$251.3858	$251.39	$251.40	$251.40
Purchase #2	$29.58	6.652%	$31.5477	$31.55	$31.55	$31.50
Purchase #3	$56.45	9.174%	$61.6287	$61.63	$61.65	$61.60
Purchase #4	$87.81	13.305%	$99.4931	$99.49	$99.50	$99.50
Purchase #5	$130.83	9.248%	$142.9292	$142.93	$142.95	$142.90
Purchase #6	$141.26	7.649%	$152.065	$152.07	$152.05	$152.10
Purchase #7	$53.83	3.743%	$55.8449	$55.84	$55.85	$55.80
7 purchase totals =	$723.61		$794.8944	$794.90	$794.95	$794.80