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	$173.77	6.601%	$185.2406	$185.24	$185.25	$185.20
Purchase #2	$46.40	8.381%	$50.2888	$50.29	$50.30	$50.30
Purchase #3	$172.95	10.306%	$190.7742	$190.77	$190.75	$190.80
Purchase #4	$139.60	9.791%	$153.2682	$153.27	$153.25	$153.30
Purchase #5	$51.69	9.323%	$56.5091	$56.51	$56.50	$56.50
Purchase #6	$110.71	12.857%	$124.944	$124.94	$124.95	$124.90
Purchase #7	$211.57	6.269%	$224.8333	$224.83	$224.85	$224.80
7 purchase totals =	$906.69		$985.8582	$985.85	$985.85	$985.80