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	$129.75	10.594%	$143.4957	$143.50	$143.50	$143.50
Purchase #2	$240.40	6.276%	$255.4875	$255.49	$255.50	$255.50
Purchase #3	$214.43	9.365%	$234.5114	$234.51	$234.50	$234.50
Purchase #4	$183.45	3.739%	$190.3092	$190.31	$190.30	$190.30
Purchase #5	$224.35	11.775%	$250.7672	$250.77	$250.75	$250.80
Purchase #6	$58.49	11.351%	$65.1292	$65.13	$65.15	$65.10
Purchase #7	$245.31	9.851%	$269.4755	$269.48	$269.50	$269.50
7 purchase totals =	$1,296.18		$1,409.1757	$1,409.19	$1,409.20	$1,409.20