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	$39.56	8.714%	$43.0073	$43.01	$43.00	$43.00
Purchase #2	$153.50	8.605%	$166.7087	$166.71	$166.70	$166.70
Purchase #3	$62.82	6.812%	$67.0993	$67.10	$67.10	$67.10
Purchase #4	$149.75	4.499%	$156.4873	$156.49	$156.50	$156.50
Purchase #5	$123.42	13.838%	$140.4989	$140.50	$140.50	$140.50
Purchase #6	$164.93	4.431%	$172.238	$172.24	$172.25	$172.20
Purchase #7	$237.30	5.540%	$250.4464	$250.45	$250.45	$250.40
7 purchase totals =	$931.28		$996.4859	$996.50	$996.50	$996.40