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	$131.39	13.333%	$148.9082	$148.91	$148.90	$148.90
Purchase #2	$179.91	11.390%	$200.4017	$200.40	$200.40	$200.40
Purchase #3	$181.52	5.776%	$192.0046	$192.00	$192.00	$192.00
Purchase #4	$13.73	4.720%	$14.3781	$14.38	$14.40	$14.40
Purchase #5	$231.96	10.124%	$255.4436	$255.44	$255.45	$255.40
Purchase #6	$96.40	3.273%	$99.5552	$99.56	$99.55	$99.60
Purchase #7	$76.43	4.364%	$79.7654	$79.77	$79.75	$79.80
7 purchase totals =	$911.34		$990.4568	$990.46	$990.45	$990.50