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	$8.40	5.583%	$8.869	$8.87	$8.85	$8.90
Purchase #2	$47.30	9.543%	$51.8138	$51.81	$51.80	$51.80
Purchase #3	$18.87	12.551%	$21.2384	$21.24	$21.25	$21.20
Purchase #4	$34.82	12.297%	$39.1018	$39.10	$39.10	$39.10
Purchase #5	$46.32	8.504%	$50.2591	$50.26	$50.25	$50.30
Purchase #6	$217.43	7.568%	$233.8851	$233.89	$233.90	$233.90
Purchase #7	$5.91	6.735%	$6.308	$6.31	$6.30	$6.30
7 purchase totals =	$379.05		$411.4752	$411.48	$411.45	$411.50