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	$234.52	12.694%	$264.29	$264.29	$264.30	$264.30
Purchase #2	$35.59	7.123%	$38.1251	$38.13	$38.15	$38.10
Purchase #3	$96.59	3.218%	$99.6983	$99.70	$99.70	$99.70
Purchase #4	$104.83	3.734%	$108.7444	$108.74	$108.75	$108.70
Purchase #5	$102.88	13.355%	$116.6196	$116.62	$116.60	$116.60
Purchase #6	$110.89	7.515%	$119.2234	$119.22	$119.20	$119.20
Purchase #7	$136.31	10.400%	$150.4862	$150.49	$150.50	$150.50
7 purchase totals =	$821.61		$897.1870	$897.19	$897.20	$897.10