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	$205.47	12.803%	$231.7763	$231.78	$231.80	$231.80
Purchase #2	$151.35	11.374%	$168.5645	$168.56	$168.55	$168.60
Purchase #3	$48.69	11.585%	$54.3307	$54.33	$54.35	$54.30
Purchase #4	$32.45	3.489%	$33.5822	$33.58	$33.60	$33.60
Purchase #5	$141.26	7.131%	$151.3333	$151.33	$151.35	$151.30
Purchase #6	$71.25	9.105%	$77.7373	$77.74	$77.75	$77.70
Purchase #7	$46.68	9.341%	$51.0404	$51.04	$51.05	$51.00
7 purchase totals =	$697.15		$768.3647	$768.36	$768.45	$768.30