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	$210.72	3.610%	$218.327	$218.33	$218.35	$218.30
Purchase #2	$166.41	11.397%	$185.3757	$185.38	$185.40	$185.40
Purchase #3	$82.94	9.556%	$90.8657	$90.87	$90.85	$90.90
Purchase #4	$70.51	13.543%	$80.0592	$80.06	$80.05	$80.10
Purchase #5	$70.75	12.312%	$79.4607	$79.46	$79.45	$79.50
Purchase #6	$97.78	6.835%	$104.4633	$104.46	$104.45	$104.50
Purchase #7	$84.52	3.699%	$87.6464	$87.65	$87.65	$87.60
7 purchase totals =	$783.63		$846.1980	$846.21	$846.20	$846.30