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	$248.51	13.180%	$281.2636	$281.26	$281.25	$281.30
Purchase #2	$11.72	9.147%	$12.792	$12.79	$12.80	$12.80
Purchase #3	$78.69	9.191%	$85.9224	$85.92	$85.90	$85.90
Purchase #4	$139.44	4.332%	$145.4805	$145.48	$145.50	$145.50
Purchase #5	$35.49	8.425%	$38.48	$38.48	$38.50	$38.50
Purchase #6	$43.38	9.212%	$47.3762	$47.38	$47.40	$47.40
Purchase #7	$242.42	6.126%	$257.2706	$257.27	$257.25	$257.30
7 purchase totals =	$799.65		$868.5853	$868.58	$868.60	$868.70