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	$55.35	3.788%	$57.4467	$57.45	$57.45	$57.40
Purchase #2	$14.72	5.123%	$15.4741	$15.47	$15.45	$15.50
Purchase #3	$208.92	9.785%	$229.3628	$229.36	$229.35	$229.40
Purchase #4	$239.66	3.425%	$247.8684	$247.87	$247.85	$247.90
Purchase #5	$234.41	6.639%	$249.9725	$249.97	$249.95	$250.00
Purchase #6	$114.46	11.742%	$127.8999	$127.90	$127.90	$127.90
Purchase #7	$50.25	5.764%	$53.1464	$53.15	$53.15	$53.10
7 purchase totals =	$917.77		$981.1708	$981.17	$981.10	$981.20