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	$15.77	5.308%	$16.6071	$16.61	$16.60	$16.60
Purchase #2	$119.82	13.401%	$135.8771	$135.88	$135.90	$135.90
Purchase #3	$89.82	6.435%	$95.5999	$95.60	$95.60	$95.60
Purchase #4	$175.72	6.716%	$187.5214	$187.52	$187.50	$187.50
Purchase #5	$106.41	4.206%	$110.8856	$110.89	$110.90	$110.90
Purchase #6	$116.57	9.695%	$127.8715	$127.87	$127.85	$127.90
Purchase #7	$25.40	13.401%	$28.8039	$28.80	$28.80	$28.80
7 purchase totals =	$649.51		$703.1665	$703.17	$703.15	$703.20