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	$34.83	7.156%	$37.3224	$37.32	$37.30	$37.30
Purchase #2	$211.91	11.873%	$237.0701	$237.07	$237.05	$237.10
Purchase #3	$229.69	13.219%	$260.0527	$260.05	$260.05	$260.10
Purchase #4	$151.58	10.285%	$167.17	$167.17	$167.15	$167.20
Purchase #5	$74.86	11.372%	$83.3731	$83.37	$83.35	$83.40
Purchase #6	$52.88	4.183%	$55.092	$55.09	$55.10	$55.10
Purchase #7	$18.79	10.648%	$20.7908	$20.79	$20.80	$20.80
7 purchase totals =	$774.54		$860.8711	$860.86	$860.80	$861.00