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	$71.76	12.614%	$80.8118	$80.81	$80.80	$80.80
Purchase #2	$215.62	3.654%	$223.4988	$223.50	$223.50	$223.50
Purchase #3	$205.27	12.284%	$230.4854	$230.49	$230.50	$230.50
Purchase #4	$34.81	7.274%	$37.3421	$37.34	$37.35	$37.30
Purchase #5	$98.38	8.608%	$106.8486	$106.85	$106.85	$106.80
Purchase #6	$224.67	9.250%	$245.452	$245.45	$245.45	$245.50
Purchase #7	$186.92	13.262%	$211.7093	$211.71	$211.70	$211.70
7 purchase totals =	$1,037.43		$1,136.1480	$1,136.15	$1,136.15	$1,136.10