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	$234.73	3.832%	$243.7249	$243.72	$243.70	$243.70
Purchase #2	$142.29	3.108%	$146.7124	$146.71	$146.70	$146.70
Purchase #3	$59.72	9.532%	$65.4125	$65.41	$65.40	$65.40
Purchase #4	$109.90	7.834%	$118.5096	$118.51	$118.50	$118.50
Purchase #5	$200.97	4.287%	$209.5856	$209.59	$209.60	$209.60
Purchase #6	$18.48	8.779%	$20.1024	$20.10	$20.10	$20.10
Purchase #7	$242.81	13.450%	$275.4679	$275.47	$275.45	$275.50
7 purchase totals =	$1,008.90		$1,079.5153	$1,079.51	$1,079.45	$1,079.50