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	$34.49	12.341%	$38.7464	$38.75	$38.75	$38.70
Purchase #2	$205.51	4.776%	$215.3252	$215.33	$215.35	$215.30
Purchase #3	$165.88	8.104%	$179.3229	$179.32	$179.30	$179.30
Purchase #4	$32.36	10.286%	$35.6885	$35.69	$35.70	$35.70
Purchase #5	$214.77	12.628%	$241.8912	$241.89	$241.90	$241.90
Purchase #6	$240.95	7.824%	$259.8019	$259.80	$259.80	$259.80
Purchase #7	$85.61	4.553%	$89.5078	$89.51	$89.50	$89.50
7 purchase totals =	$979.57		$1,060.2839	$1,060.29	$1,060.30	$1,060.20