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	$94.29	3.422%	$97.5166	$97.52	$97.50	$97.50
Purchase #2	$32.41	12.778%	$36.5513	$36.55	$36.55	$36.60
Purchase #3	$29.88	5.750%	$31.5981	$31.60	$31.60	$31.60
Purchase #4	$79.73	8.668%	$86.641	$86.64	$86.65	$86.60
Purchase #5	$37.53	11.654%	$41.9037	$41.90	$41.90	$41.90
Purchase #6	$116.72	13.680%	$132.6873	$132.69	$132.70	$132.70
Purchase #7	$135.42	11.496%	$150.9879	$150.99	$151.00	$151.00
7 purchase totals =	$525.98		$577.8859	$577.89	$577.90	$577.90