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	$137.89	5.606%	$145.6201	$145.62	$145.60	$145.60
Purchase #2	$31.69	13.554%	$35.9853	$35.99	$36.00	$36.00
Purchase #3	$159.63	6.668%	$170.2741	$170.27	$170.25	$170.30
Purchase #4	$40.67	10.548%	$44.9599	$44.96	$44.95	$45.00
Purchase #5	$95.28	5.784%	$100.791	$100.79	$100.80	$100.80
Purchase #6	$78.59	4.665%	$82.2562	$82.26	$82.25	$82.30
Purchase #7	$105.38	12.211%	$118.248	$118.25	$118.25	$118.20
7 purchase totals =	$649.13		$698.1346	$698.14	$698.10	$698.20