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	$18.77	7.321%	$20.1442	$20.14	$20.15	$20.10
Purchase #2	$99.57	10.260%	$109.7859	$109.79	$109.80	$109.80
Purchase #3	$49.54	8.207%	$53.6057	$53.61	$53.60	$53.60
Purchase #4	$127.71	3.801%	$132.5643	$132.56	$132.55	$132.60
Purchase #5	$130.89	13.149%	$148.1007	$148.10	$148.10	$148.10
Purchase #6	$151.35	12.398%	$170.1144	$170.11	$170.10	$170.10
Purchase #7	$86.51	10.375%	$95.4854	$95.49	$95.50	$95.50
7 purchase totals =	$664.34		$729.8006	$729.80	$729.80	$729.80