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	$24.60	13.252%	$27.86	$27.86	$27.85	$27.90
Purchase #2	$26.88	5.572%	$28.3778	$28.38	$28.40	$28.40
Purchase #3	$236.50	3.394%	$244.5268	$244.53	$244.55	$244.50
Purchase #4	$34.29	13.335%	$38.8626	$38.86	$38.85	$38.90
Purchase #5	$159.60	3.632%	$165.3967	$165.40	$165.40	$165.40
Purchase #6	$82.36	9.639%	$90.2987	$90.30	$90.30	$90.30
Purchase #7	$224.95	7.766%	$242.4196	$242.42	$242.40	$242.40
7 purchase totals =	$789.18		$837.7422	$837.75	$837.75	$837.80