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	$222.72	8.670%	$242.0298	$242.03	$242.05	$242.00
Purchase #2	$59.92	12.588%	$67.4627	$67.46	$67.45	$67.50
Purchase #3	$136.55	3.129%	$140.8226	$140.82	$140.80	$140.80
Purchase #4	$81.86	4.466%	$85.5159	$85.52	$85.50	$85.50
Purchase #5	$133.74	4.285%	$139.4708	$139.47	$139.45	$139.50
Purchase #6	$143.49	13.343%	$162.6359	$162.64	$162.65	$162.60
Purchase #7	$50.84	8.451%	$55.1365	$55.14	$55.15	$55.10
7 purchase totals =	$829.12		$893.0742	$893.08	$893.05	$893.00