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	$234.38	6.617%	$249.8889	$249.89	$249.90	$249.90
Purchase #2	$17.81	4.644%	$18.6371	$18.64	$18.65	$18.60
Purchase #3	$23.41	4.810%	$24.536	$24.54	$24.55	$24.50
Purchase #4	$125.83	5.493%	$132.7418	$132.74	$132.75	$132.70
Purchase #5	$82.63	4.253%	$86.1443	$86.14	$86.15	$86.10
Purchase #6	$76.87	8.618%	$83.4947	$83.49	$83.50	$83.50
Purchase #7	$79.56	4.802%	$83.3805	$83.38	$83.40	$83.40
7 purchase totals =	$640.49		$678.8233	$678.82	$678.90	$678.70