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	$100.33	11.210%	$111.577	$111.58	$111.60	$111.60
Purchase #2	$27.94	10.598%	$30.9011	$30.90	$30.90	$30.90
Purchase #3	$27.48	11.738%	$30.7056	$30.71	$30.70	$30.70
Purchase #4	$55.76	3.133%	$57.507	$57.51	$57.50	$57.50
Purchase #5	$100.88	4.563%	$105.4832	$105.48	$105.50	$105.50
Purchase #6	$227.58	8.165%	$246.1619	$246.16	$246.15	$246.20
Purchase #7	$12.25	9.275%	$13.3862	$13.39	$13.40	$13.40
7 purchase totals =	$552.22		$595.7220	$595.73	$595.75	$595.80