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	$98.93	10.466%	$109.284	$109.28	$109.30	$109.30
Purchase #2	$127.60	9.629%	$139.8866	$139.89	$139.90	$139.90
Purchase #3	$224.87	7.296%	$241.2765	$241.28	$241.30	$241.30
Purchase #4	$33.91	11.714%	$37.8822	$37.88	$37.90	$37.90
Purchase #5	$29.93	4.646%	$31.3205	$31.32	$31.30	$31.30
Purchase #6	$169.37	3.130%	$174.6713	$174.67	$174.65	$174.70
Purchase #7	$94.61	8.508%	$102.6594	$102.66	$102.65	$102.70
7 purchase totals =	$779.22		$836.9805	$836.98	$837.00	$837.10