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	$171.98	6.555%	$183.2533	$183.25	$183.25	$183.30
Purchase #2	$162.35	13.468%	$184.2153	$184.22	$184.20	$184.20
Purchase #3	$75.99	8.714%	$82.6118	$82.61	$82.60	$82.60
Purchase #4	$82.91	4.434%	$86.5862	$86.59	$86.60	$86.60
Purchase #5	$44.28	13.275%	$50.1582	$50.16	$50.15	$50.20
Purchase #6	$145.89	11.527%	$162.7067	$162.71	$162.70	$162.70
Purchase #7	$91.96	9.503%	$100.699	$100.70	$100.70	$100.70
7 purchase totals =	$775.36		$850.2305	$850.24	$850.20	$850.30