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	$200.58	6.397%	$213.4111	$213.41	$213.40	$213.40
Purchase #2	$150.28	11.750%	$167.9379	$167.94	$167.95	$167.90
Purchase #3	$54.93	8.658%	$59.6858	$59.69	$59.70	$59.70
Purchase #4	$74.25	10.655%	$82.1613	$82.16	$82.15	$82.20
Purchase #5	$174.43	7.542%	$187.5855	$187.59	$187.60	$187.60
Purchase #6	$101.76	10.214%	$112.1538	$112.15	$112.15	$112.20
Purchase #7	$73.72	6.480%	$78.4971	$78.50	$78.50	$78.50
7 purchase totals =	$829.95		$901.4325	$901.44	$901.45	$901.50