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	$5.35	4.868%	$5.6104	$5.61	$5.60	$5.60
Purchase #2	$18.85	4.590%	$19.7152	$19.72	$19.70	$19.70
Purchase #3	$139.88	10.385%	$154.4065	$154.41	$154.40	$154.40
Purchase #4	$106.92	11.585%	$119.3067	$119.31	$119.30	$119.30
Purchase #5	$98.28	13.557%	$111.6038	$111.60	$111.60	$111.60
Purchase #6	$151.88	8.185%	$164.3114	$164.31	$164.30	$164.30
Purchase #7	$35.51	6.515%	$37.8235	$37.82	$37.80	$37.80
7 purchase totals =	$556.67		$612.7775	$612.78	$612.70	$612.70