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	$12.48	5.189%	$13.1276	$13.13	$13.15	$13.10
Purchase #2	$204.32	7.610%	$219.8688	$219.87	$219.85	$219.90
Purchase #3	$85.49	4.593%	$89.4166	$89.42	$89.40	$89.40
Purchase #4	$38.32	7.662%	$41.2561	$41.26	$41.25	$41.30
Purchase #5	$69.49	6.261%	$73.8408	$73.84	$73.85	$73.80
Purchase #6	$118.42	12.154%	$132.8128	$132.81	$132.80	$132.80
Purchase #7	$18.76	8.292%	$20.3156	$20.32	$20.30	$20.30
7 purchase totals =	$547.28		$590.6383	$590.65	$590.60	$590.60