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	$185.27	3.402%	$191.5729	$191.57	$191.55	$191.60
Purchase #2	$85.60	7.678%	$92.1724	$92.17	$92.15	$92.20
Purchase #3	$59.29	10.484%	$65.506	$65.51	$65.50	$65.50
Purchase #4	$208.55	6.390%	$221.8763	$221.88	$221.90	$221.90
Purchase #5	$47.95	9.530%	$52.5196	$52.52	$52.50	$52.50
Purchase #6	$64.80	9.443%	$70.9191	$70.92	$70.90	$70.90
Purchase #7	$145.95	10.552%	$161.3506	$161.35	$161.35	$161.40
7 purchase totals =	$797.41		$855.9169	$855.92	$855.85	$856.00