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	$37.61	5.436%	$39.6545	$39.65	$39.65	$39.70
Purchase #2	$110.74	13.683%	$125.8926	$125.89	$125.90	$125.90
Purchase #3	$147.62	12.146%	$165.5499	$165.55	$165.55	$165.50
Purchase #4	$107.45	6.262%	$114.1785	$114.18	$114.20	$114.20
Purchase #5	$101.75	3.352%	$105.1607	$105.16	$105.15	$105.20
Purchase #6	$213.32	10.874%	$236.5164	$236.52	$236.50	$236.50
Purchase #7	$216.32	6.150%	$229.6237	$229.62	$229.60	$229.60
7 purchase totals =	$934.81		$1,016.5763	$1,016.57	$1,016.55	$1,016.60