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	$76.32	11.578%	$85.1563	$85.16	$85.15	$85.20
Purchase #2	$116.48	10.212%	$128.3749	$128.37	$128.35	$128.40
Purchase #3	$166.30	12.474%	$187.0443	$187.04	$187.05	$187.00
Purchase #4	$174.67	13.842%	$198.8478	$198.85	$198.85	$198.80
Purchase #5	$138.87	9.684%	$152.3182	$152.32	$152.30	$152.30
Purchase #6	$75.49	4.588%	$78.9535	$78.95	$78.95	$79.00
Purchase #7	$57.90	6.247%	$61.517	$61.52	$61.50	$61.50
7 purchase totals =	$806.03		$892.2120	$892.21	$892.15	$892.20