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	$221.77	4.491%	$231.7297	$231.73	$231.75	$231.70
Purchase #2	$192.53	10.410%	$212.5724	$212.57	$212.55	$212.60
Purchase #3	$88.29	12.706%	$99.5081	$99.51	$99.50	$99.50
Purchase #4	$88.36	13.700%	$100.4653	$100.47	$100.45	$100.50
Purchase #5	$103.77	3.489%	$107.3905	$107.39	$107.40	$107.40
Purchase #6	$78.95	11.867%	$88.319	$88.32	$88.30	$88.30
Purchase #7	$90.84	11.406%	$101.2012	$101.20	$101.20	$101.20
7 purchase totals =	$864.51		$941.1862	$941.19	$941.15	$941.20