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	$28.94	13.730%	$32.9135	$32.91	$32.90	$32.90
Purchase #2	$89.31	12.347%	$100.3371	$100.34	$100.35	$100.30
Purchase #3	$25.86	12.540%	$29.1028	$29.10	$29.10	$29.10
Purchase #4	$238.71	10.820%	$264.5384	$264.54	$264.55	$264.50
Purchase #5	$86.39	7.665%	$93.0118	$93.01	$93.00	$93.00
Purchase #6	$46.34	5.339%	$48.8141	$48.81	$48.80	$48.80
Purchase #7	$93.47	12.845%	$105.4762	$105.48	$105.50	$105.50
7 purchase totals =	$609.02		$674.1939	$674.19	$674.20	$674.10