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	$107.86	3.426%	$111.5553	$111.56	$111.55	$111.60
Purchase #2	$99.42	10.466%	$109.8253	$109.83	$109.85	$109.80
Purchase #3	$72.74	9.342%	$79.5354	$79.54	$79.55	$79.50
Purchase #4	$106.57	12.115%	$119.481	$119.48	$119.50	$119.50
Purchase #5	$22.76	8.106%	$24.6049	$24.60	$24.60	$24.60
Purchase #6	$32.28	6.414%	$34.3504	$34.35	$34.35	$34.40
Purchase #7	$52.90	11.137%	$58.7915	$58.79	$58.80	$58.80
7 purchase totals =	$494.53		$538.1438	$538.15	$538.20	$538.20