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	$192.47	12.287%	$216.1188	$216.12	$216.10	$216.10
Purchase #2	$37.37	7.488%	$40.1683	$40.17	$40.15	$40.20
Purchase #3	$10.52	8.210%	$11.3837	$11.38	$11.40	$11.40
Purchase #4	$17.61	5.390%	$18.5592	$18.56	$18.55	$18.60
Purchase #5	$216.59	8.176%	$234.2984	$234.30	$234.30	$234.30
Purchase #6	$48.99	11.811%	$54.7762	$54.78	$54.80	$54.80
Purchase #7	$161.84	3.739%	$167.8912	$167.89	$167.90	$167.90
7 purchase totals =	$685.39		$743.1958	$743.20	$743.20	$743.30