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	$202.39	12.259%	$227.201	$227.20	$227.20	$227.20
Purchase #2	$65.27	9.327%	$71.3577	$71.36	$71.35	$71.40
Purchase #3	$173.37	5.321%	$182.595	$182.60	$182.60	$182.60
Purchase #4	$53.25	4.325%	$55.5531	$55.55	$55.55	$55.60
Purchase #5	$228.55	9.604%	$250.4999	$250.50	$250.50	$250.50
Purchase #6	$148.84	12.527%	$167.4852	$167.49	$167.50	$167.50
Purchase #7	$42.92	4.473%	$44.8398	$44.84	$44.85	$44.80
7 purchase totals =	$914.59		$999.5317	$999.54	$999.55	$999.60