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	$181.28	9.680%	$198.8279	$198.83	$198.85	$198.80
Purchase #2	$202.95	11.871%	$227.0422	$227.04	$227.05	$227.00
Purchase #3	$145.38	10.625%	$160.8266	$160.83	$160.85	$160.80
Purchase #4	$25.45	9.538%	$27.8774	$27.88	$27.90	$27.90
Purchase #5	$50.74	4.828%	$53.1897	$53.19	$53.20	$53.20
Purchase #6	$84.94	6.624%	$90.5664	$90.57	$90.55	$90.60
Purchase #7	$46.73	3.295%	$48.2698	$48.27	$48.25	$48.30
7 purchase totals =	$737.47		$806.6000	$806.61	$806.65	$806.60