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	$221.66	13.458%	$251.491	$251.49	$251.50	$251.50
Purchase #2	$112.81	13.499%	$128.0382	$128.04	$128.05	$128.00
Purchase #3	$93.41	4.402%	$97.5219	$97.52	$97.50	$97.50
Purchase #4	$88.78	4.156%	$92.4697	$92.47	$92.45	$92.50
Purchase #5	$96.69	3.609%	$100.1795	$100.18	$100.20	$100.20
Purchase #6	$91.46	5.257%	$96.2681	$96.27	$96.25	$96.30
Purchase #7	$154.48	3.485%	$159.8636	$159.86	$159.85	$159.90
7 purchase totals =	$859.29		$925.8320	$925.83	$925.80	$925.90