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	$128.63	10.608%	$142.2751	$142.28	$142.30	$142.30
Purchase #2	$34.42	8.629%	$37.3901	$37.39	$37.40	$37.40
Purchase #3	$37.84	3.635%	$39.2155	$39.22	$39.20	$39.20
Purchase #4	$239.68	13.406%	$271.8115	$271.81	$271.80	$271.80
Purchase #5	$247.45	11.470%	$275.8325	$275.83	$275.85	$275.80
Purchase #6	$59.74	12.532%	$67.2266	$67.23	$67.25	$67.20
Purchase #7	$138.53	3.117%	$142.848	$142.85	$142.85	$142.80
7 purchase totals =	$886.29		$976.5993	$976.61	$976.65	$976.50