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	$173.76	6.670%	$185.3498	$185.35	$185.35	$185.30
Purchase #2	$246.81	6.512%	$262.8823	$262.88	$262.90	$262.90
Purchase #3	$204.45	8.499%	$221.8262	$221.83	$221.85	$221.80
Purchase #4	$187.39	6.461%	$199.4973	$199.50	$199.50	$199.50
Purchase #5	$32.49	12.217%	$36.4593	$36.46	$36.45	$36.50
Purchase #6	$200.70	11.685%	$224.1518	$224.15	$224.15	$224.20
Purchase #7	$36.93	13.731%	$42.0009	$42.00	$42.00	$42.00
7 purchase totals =	$1,082.53		$1,172.1676	$1,172.17	$1,172.20	$1,172.20