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	$33.57	13.606%	$38.1375	$38.14	$38.15	$38.10
Purchase #2	$26.88	12.766%	$30.3115	$30.31	$30.30	$30.30
Purchase #3	$112.47	5.801%	$118.9944	$118.99	$119.00	$119.00
Purchase #4	$30.77	5.206%	$32.3719	$32.37	$32.35	$32.40
Purchase #5	$73.67	13.671%	$83.7414	$83.74	$83.75	$83.70
Purchase #6	$86.33	5.281%	$90.8891	$90.89	$90.90	$90.90
Purchase #7	$156.44	11.177%	$173.9253	$173.93	$173.95	$173.90
7 purchase totals =	$520.13		$568.3711	$568.37	$568.40	$568.30