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	$154.66	3.831%	$160.585	$160.59	$160.60	$160.60
Purchase #2	$241.78	11.333%	$269.1809	$269.18	$269.20	$269.20
Purchase #3	$90.41	8.664%	$98.2431	$98.24	$98.25	$98.20
Purchase #4	$25.97	10.227%	$28.626	$28.63	$28.65	$28.60
Purchase #5	$101.71	10.301%	$112.1871	$112.19	$112.20	$112.20
Purchase #6	$53.52	11.695%	$59.7792	$59.78	$59.80	$59.80
Purchase #7	$215.30	4.851%	$225.7442	$225.74	$225.75	$225.70
7 purchase totals =	$883.35		$954.3455	$954.35	$954.45	$954.30