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	$127.85	8.663%	$138.9256	$138.93	$138.95	$138.90
Purchase #2	$149.96	3.459%	$155.1471	$155.15	$155.15	$155.10
Purchase #3	$79.66	7.803%	$85.8759	$85.88	$85.90	$85.90
Purchase #4	$113.78	11.131%	$126.4449	$126.44	$126.45	$126.40
Purchase #5	$53.58	11.486%	$59.7342	$59.73	$59.75	$59.70
Purchase #6	$129.58	9.177%	$141.4716	$141.47	$141.45	$141.50
Purchase #7	$144.78	4.617%	$151.4645	$151.46	$151.45	$151.50
7 purchase totals =	$799.19		$859.0638	$859.06	$859.10	$859.00