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	$56.86	6.125%	$60.3427	$60.34	$60.35	$60.30
Purchase #2	$232.87	6.759%	$248.6097	$248.61	$248.60	$248.60
Purchase #3	$52.26	3.625%	$54.1544	$54.15	$54.15	$54.20
Purchase #4	$18.51	10.649%	$20.4811	$20.48	$20.50	$20.50
Purchase #5	$74.88	4.843%	$78.5064	$78.51	$78.50	$78.50
Purchase #6	$248.64	5.447%	$262.1834	$262.18	$262.20	$262.20
Purchase #7	$50.96	9.551%	$55.8272	$55.83	$55.85	$55.80
7 purchase totals =	$734.98		$780.1049	$780.10	$780.15	$780.10