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	$102.93	8.828%	$112.0167	$112.02	$112.00	$112.00
Purchase #2	$126.37	12.515%	$142.1852	$142.19	$142.20	$142.20
Purchase #3	$31.63	11.487%	$35.2633	$35.26	$35.25	$35.30
Purchase #4	$50.36	9.762%	$55.2761	$55.28	$55.30	$55.30
Purchase #5	$99.55	6.379%	$105.9003	$105.90	$105.90	$105.90
Purchase #6	$18.86	7.514%	$20.2771	$20.28	$20.30	$20.30
Purchase #7	$173.34	11.287%	$192.9049	$192.90	$192.90	$192.90
7 purchase totals =	$603.04		$663.8236	$663.83	$663.85	$663.90