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	$68.87	6.130%	$73.0917	$73.09	$73.10	$73.10
Purchase #2	$29.49	10.228%	$32.5062	$32.51	$32.50	$32.50
Purchase #3	$229.91	5.166%	$241.7872	$241.79	$241.80	$241.80
Purchase #4	$90.93	10.528%	$100.5031	$100.50	$100.50	$100.50
Purchase #5	$89.37	11.251%	$99.425	$99.43	$99.45	$99.40
Purchase #6	$102.71	11.787%	$114.8164	$114.82	$114.80	$114.80
Purchase #7	$241.73	5.374%	$254.7206	$254.72	$254.70	$254.70
7 purchase totals =	$853.01		$916.8502	$916.86	$916.85	$916.80