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	$114.80	11.165%	$127.6174	$127.62	$127.60	$127.60
Purchase #2	$172.59	11.503%	$192.443	$192.44	$192.45	$192.40
Purchase #3	$222.73	12.258%	$250.0322	$250.03	$250.05	$250.00
Purchase #4	$24.26	13.681%	$27.579	$27.58	$27.60	$27.60
Purchase #5	$38.95	13.436%	$44.1833	$44.18	$44.20	$44.20
Purchase #6	$35.91	12.841%	$40.5212	$40.52	$40.50	$40.50
Purchase #7	$228.93	7.625%	$246.3859	$246.39	$246.40	$246.40
7 purchase totals =	$838.17		$928.7620	$928.76	$928.80	$928.70