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	$20.26	6.562%	$21.5895	$21.59	$21.60	$21.60
Purchase #2	$138.37	9.447%	$151.4418	$151.44	$151.45	$151.40
Purchase #3	$120.45	3.185%	$124.2863	$124.29	$124.30	$124.30
Purchase #4	$191.57	9.827%	$210.3956	$210.40	$210.40	$210.40
Purchase #5	$171.82	7.512%	$184.7271	$184.73	$184.75	$184.70
Purchase #6	$45.61	7.574%	$49.0645	$49.06	$49.05	$49.10
Purchase #7	$228.43	11.650%	$255.0421	$255.04	$255.05	$255.00
7 purchase totals =	$916.51		$996.5469	$996.55	$996.60	$996.50