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	$52.46	13.867%	$59.7346	$59.73	$59.75	$59.70
Purchase #2	$101.92	9.398%	$111.4984	$111.50	$111.50	$111.50
Purchase #3	$72.53	10.523%	$80.1623	$80.16	$80.15	$80.20
Purchase #4	$106.60	13.303%	$120.781	$120.78	$120.80	$120.80
Purchase #5	$13.81	7.292%	$14.817	$14.82	$14.80	$14.80
Purchase #6	$189.59	8.787%	$206.2493	$206.25	$206.25	$206.20
Purchase #7	$71.44	3.639%	$74.0397	$74.04	$74.05	$74.00
7 purchase totals =	$608.35		$667.2823	$667.28	$667.30	$667.20