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	$108.51	13.632%	$123.3021	$123.30	$123.30	$123.30
Purchase #2	$195.86	10.738%	$216.8914	$216.89	$216.90	$216.90
Purchase #3	$140.90	4.509%	$147.2532	$147.25	$147.25	$147.30
Purchase #4	$144.86	10.269%	$159.7357	$159.74	$159.75	$159.70
Purchase #5	$164.51	7.684%	$177.1509	$177.15	$177.15	$177.20
Purchase #6	$202.28	13.511%	$229.6101	$229.61	$229.60	$229.60
Purchase #7	$131.81	11.454%	$146.9075	$146.91	$146.90	$146.90
7 purchase totals =	$1,088.73		$1,200.8509	$1,200.85	$1,200.85	$1,200.90