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	$81.56	10.497%	$90.1214	$90.12	$90.10	$90.10
Purchase #2	$194.32	12.838%	$219.2668	$219.27	$219.25	$219.30
Purchase #3	$235.99	10.232%	$260.1365	$260.14	$260.15	$260.10
Purchase #4	$205.97	11.303%	$229.2508	$229.25	$229.25	$229.30
Purchase #5	$26.64	10.865%	$29.5344	$29.53	$29.55	$29.50
Purchase #6	$192.29	4.171%	$200.3104	$200.31	$200.30	$200.30
Purchase #7	$38.83	10.589%	$42.9417	$42.94	$42.95	$42.90
7 purchase totals =	$975.60		$1,071.5620	$1,071.56	$1,071.55	$1,071.50