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	$185.27	12.410%	$208.262	$208.26	$208.25	$208.30
Purchase #2	$40.38	4.607%	$42.2403	$42.24	$42.25	$42.20
Purchase #3	$27.74	13.241%	$31.4131	$31.41	$31.40	$31.40
Purchase #4	$205.82	8.721%	$223.7696	$223.77	$223.75	$223.80
Purchase #5	$123.41	13.109%	$139.5878	$139.59	$139.60	$139.60
Purchase #6	$5.54	4.598%	$5.7947	$5.79	$5.80	$5.80
Purchase #7	$78.62	10.765%	$87.0834	$87.08	$87.10	$87.10
7 purchase totals =	$666.78		$738.1509	$738.14	$738.15	$738.20