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	$237.58	4.664%	$248.6607	$248.66	$248.65	$248.70
Purchase #2	$153.50	12.514%	$172.709	$172.71	$172.70	$172.70
Purchase #3	$94.45	6.585%	$100.6695	$100.67	$100.65	$100.70
Purchase #4	$170.83	13.599%	$194.0612	$194.06	$194.05	$194.10
Purchase #5	$86.50	10.553%	$95.6283	$95.63	$95.65	$95.60
Purchase #6	$25.27	10.723%	$27.9797	$27.98	$28.00	$28.00
Purchase #7	$215.28	12.515%	$242.2223	$242.22	$242.20	$242.20
7 purchase totals =	$983.41		$1,081.9307	$1,081.93	$1,081.90	$1,082.00