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	$72.76	8.114%	$78.6637	$78.66	$78.65	$78.70
Purchase #2	$28.26	9.764%	$31.0193	$31.02	$31.00	$31.00
Purchase #3	$214.51	12.240%	$240.766	$240.77	$240.75	$240.80
Purchase #4	$194.50	7.401%	$208.8949	$208.89	$208.90	$208.90
Purchase #5	$102.32	12.730%	$115.3453	$115.35	$115.35	$115.30
Purchase #6	$62.35	5.247%	$65.6215	$65.62	$65.60	$65.60
Purchase #7	$243.86	6.386%	$259.4329	$259.43	$259.45	$259.40
7 purchase totals =	$918.56		$999.7436	$999.74	$999.70	$999.70