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	$27.89	11.519%	$31.1026	$31.10	$31.10	$31.10
Purchase #2	$219.59	11.610%	$245.0844	$245.08	$245.10	$245.10
Purchase #3	$185.25	12.159%	$207.7745	$207.77	$207.75	$207.80
Purchase #4	$153.50	12.137%	$172.1303	$172.13	$172.15	$172.10
Purchase #5	$55.69	9.240%	$60.8358	$60.84	$60.85	$60.80
Purchase #6	$32.59	4.222%	$33.9659	$33.97	$33.95	$34.00
Purchase #7	$158.69	5.167%	$166.8895	$166.89	$166.90	$166.90
7 purchase totals =	$833.20		$917.7830	$917.78	$917.80	$917.80