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	$207.81	6.448%	$221.2096	$221.21	$221.20	$221.20
Purchase #2	$192.30	8.625%	$208.8859	$208.89	$208.90	$208.90
Purchase #3	$86.73	11.276%	$96.5097	$96.51	$96.50	$96.50
Purchase #4	$34.40	9.257%	$37.5844	$37.58	$37.60	$37.60
Purchase #5	$104.82	13.792%	$119.2768	$119.28	$119.30	$119.30
Purchase #6	$47.42	3.531%	$49.0944	$49.09	$49.10	$49.10
Purchase #7	$96.46	9.355%	$105.4838	$105.48	$105.50	$105.50
7 purchase totals =	$769.94		$838.0446	$838.04	$838.10	$838.10