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	$57.64	6.194%	$61.2102	$61.21	$61.20	$61.20
Purchase #2	$129.35	4.200%	$134.7827	$134.78	$134.80	$134.80
Purchase #3	$89.29	3.734%	$92.6241	$92.62	$92.60	$92.60
Purchase #4	$88.29	12.763%	$99.5585	$99.56	$99.55	$99.60
Purchase #5	$86.64	4.504%	$90.5423	$90.54	$90.55	$90.50
Purchase #6	$19.25	12.799%	$21.7138	$21.71	$21.70	$21.70
Purchase #7	$240.95	11.691%	$269.1195	$269.12	$269.10	$269.10
7 purchase totals =	$711.41		$769.5511	$769.54	$769.50	$769.50