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	$218.81	10.806%	$242.4546	$242.45	$242.45	$242.50
Purchase #2	$74.33	7.449%	$79.8668	$79.87	$79.85	$79.90
Purchase #3	$171.73	10.344%	$189.4938	$189.49	$189.50	$189.50
Purchase #4	$167.58	5.143%	$176.1986	$176.20	$176.20	$176.20
Purchase #5	$156.59	3.189%	$161.5837	$161.58	$161.60	$161.60
Purchase #6	$71.43	9.349%	$78.108	$78.11	$78.10	$78.10
Purchase #7	$40.69	5.385%	$42.8812	$42.88	$42.90	$42.90
7 purchase totals =	$901.16		$970.5867	$970.58	$970.60	$970.70