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	$83.68	7.538%	$89.9878	$89.99	$90.00	$90.00
Purchase #2	$214.77	4.817%	$225.1155	$225.12	$225.10	$225.10
Purchase #3	$123.89	8.409%	$134.3079	$134.31	$134.30	$134.30
Purchase #4	$56.56	5.678%	$59.7715	$59.77	$59.75	$59.80
Purchase #5	$224.94	6.382%	$239.2957	$239.30	$239.30	$239.30
Purchase #6	$91.90	8.691%	$99.887	$99.89	$99.90	$99.90
Purchase #7	$18.35	8.620%	$19.9318	$19.93	$19.95	$19.90
7 purchase totals =	$814.09		$868.2972	$868.31	$868.30	$868.30