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	$138.31	6.221%	$146.9143	$146.91	$146.90	$146.90
Purchase #2	$181.89	8.116%	$196.6522	$196.65	$196.65	$196.70
Purchase #3	$85.68	4.303%	$89.3668	$89.37	$89.35	$89.40
Purchase #4	$231.36	13.813%	$263.3178	$263.32	$263.30	$263.30
Purchase #5	$248.28	7.507%	$266.9184	$266.92	$266.90	$266.90
Purchase #6	$14.40	10.266%	$15.8783	$15.88	$15.90	$15.90
Purchase #7	$11.43	4.580%	$11.9535	$11.95	$11.95	$12.00
7 purchase totals =	$911.35		$991.0013	$991.00	$990.95	$991.10