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	$77.97	4.556%	$81.5223	$81.52	$81.50	$81.50
Purchase #2	$152.48	13.229%	$172.6516	$172.65	$172.65	$172.70
Purchase #3	$181.72	13.253%	$205.8034	$205.80	$205.80	$205.80
Purchase #4	$154.96	3.223%	$159.9544	$159.95	$159.95	$160.00
Purchase #5	$144.26	13.706%	$164.0323	$164.03	$164.05	$164.00
Purchase #6	$185.39	12.755%	$209.0365	$209.04	$209.05	$209.00
Purchase #7	$230.25	11.449%	$256.6113	$256.61	$256.60	$256.60
7 purchase totals =	$1,127.03		$1,249.6118	$1,249.60	$1,249.60	$1,249.60