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	$221.50	10.556%	$244.8815	$244.88	$244.90	$244.90
Purchase #2	$89.70	13.520%	$101.8274	$101.83	$101.85	$101.80
Purchase #3	$22.49	10.241%	$24.7932	$24.79	$24.80	$24.80
Purchase #4	$115.96	8.866%	$126.241	$126.24	$126.25	$126.20
Purchase #5	$191.79	9.147%	$209.333	$209.33	$209.35	$209.30
Purchase #6	$57.35	3.863%	$59.5654	$59.57	$59.55	$59.60
Purchase #7	$33.69	5.391%	$35.5062	$35.51	$35.50	$35.50
7 purchase totals =	$732.48		$802.1477	$802.15	$802.20	$802.10