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	$5.55	10.536%	$6.1347	$6.13	$6.15	$6.10
Purchase #2	$247.71	5.497%	$261.3266	$261.33	$261.35	$261.30
Purchase #3	$105.79	3.624%	$109.6238	$109.62	$109.60	$109.60
Purchase #4	$229.76	3.620%	$238.0773	$238.08	$238.10	$238.10
Purchase #5	$56.54	5.173%	$59.4648	$59.46	$59.45	$59.50
Purchase #6	$108.94	3.510%	$112.7638	$112.76	$112.75	$112.80
Purchase #7	$16.75	11.444%	$18.6669	$18.67	$18.65	$18.70
7 purchase totals =	$771.04		$806.0579	$806.05	$806.05	$806.10