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	$35.83	9.129%	$39.1009	$39.10	$39.10	$39.10
Purchase #2	$143.58	11.318%	$159.8304	$159.83	$159.85	$159.80
Purchase #3	$152.74	4.362%	$159.4025	$159.40	$159.40	$159.40
Purchase #4	$176.60	7.801%	$190.3766	$190.38	$190.40	$190.40
Purchase #5	$174.33	6.583%	$185.8061	$185.81	$185.80	$185.80
Purchase #6	$161.48	3.331%	$166.8589	$166.86	$166.85	$166.90
Purchase #7	$46.91	9.530%	$51.3805	$51.38	$51.40	$51.40
7 purchase totals =	$891.47		$952.7559	$952.76	$952.80	$952.80