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	$189.28	4.403%	$197.614	$197.61	$197.60	$197.60
Purchase #2	$178.40	4.164%	$185.8286	$185.83	$185.85	$185.80
Purchase #3	$84.35	13.595%	$95.8174	$95.82	$95.80	$95.80
Purchase #4	$233.91	3.453%	$241.9869	$241.99	$242.00	$242.00
Purchase #5	$77.90	6.185%	$82.7181	$82.72	$82.70	$82.70
Purchase #6	$100.38	10.308%	$110.7272	$110.73	$110.75	$110.70
Purchase #7	$54.96	8.786%	$59.7888	$59.79	$59.80	$59.80
7 purchase totals =	$919.18		$974.4810	$974.49	$974.50	$974.40