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	$189.69	4.141%	$197.5451	$197.55	$197.55	$197.50
Purchase #2	$78.75	4.577%	$82.3544	$82.35	$82.35	$82.40
Purchase #3	$206.95	6.433%	$220.2631	$220.26	$220.25	$220.30
Purchase #4	$78.77	6.128%	$83.597	$83.60	$83.60	$83.60
Purchase #5	$149.47	6.577%	$159.3006	$159.30	$159.30	$159.30
Purchase #6	$12.86	7.376%	$13.8086	$13.81	$13.80	$13.80
Purchase #7	$78.62	4.845%	$82.4291	$82.43	$82.45	$82.40
7 purchase totals =	$795.11		$839.2979	$839.30	$839.30	$839.30