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	$249.43	9.419%	$272.9238	$272.92	$272.90	$272.90
Purchase #2	$178.32	10.261%	$196.6174	$196.62	$196.60	$196.60
Purchase #3	$9.54	4.661%	$9.9847	$9.98	$10.00	$10.00
Purchase #4	$142.79	5.594%	$150.7777	$150.78	$150.80	$150.80
Purchase #5	$206.79	11.160%	$229.8678	$229.87	$229.85	$229.90
Purchase #6	$92.86	13.652%	$105.5372	$105.54	$105.55	$105.50
Purchase #7	$123.58	3.674%	$128.1203	$128.12	$128.10	$128.10
7 purchase totals =	$1,003.31		$1,093.8289	$1,093.83	$1,093.80	$1,093.80