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	$159.67	6.839%	$170.5898	$170.59	$170.60	$170.60
Purchase #2	$196.66	13.503%	$223.215	$223.22	$223.20	$223.20
Purchase #3	$180.86	3.338%	$186.8971	$186.90	$186.90	$186.90
Purchase #4	$164.49	4.526%	$171.9348	$171.93	$171.95	$171.90
Purchase #5	$58.69	4.501%	$61.3316	$61.33	$61.35	$61.30
Purchase #6	$154.52	11.423%	$172.1708	$172.17	$172.15	$172.20
Purchase #7	$172.67	12.821%	$194.808	$194.81	$194.80	$194.80
7 purchase totals =	$1,087.56		$1,180.9471	$1,180.95	$1,180.95	$1,180.90