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	$16.51	11.291%	$18.3741	$18.37	$18.35	$18.40
Purchase #2	$35.85	13.543%	$40.7052	$40.71	$40.70	$40.70
Purchase #3	$148.44	5.762%	$156.9931	$156.99	$157.00	$157.00
Purchase #4	$101.47	9.531%	$111.1411	$111.14	$111.15	$111.10
Purchase #5	$169.35	11.387%	$188.6339	$188.63	$188.65	$188.60
Purchase #6	$124.73	3.276%	$128.8162	$128.82	$128.80	$128.80
Purchase #7	$162.26	6.357%	$172.5749	$172.57	$172.55	$172.60
7 purchase totals =	$758.61		$817.2385	$817.23	$817.20	$817.20