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	$62.53	12.508%	$70.3513	$70.35	$70.35	$70.40
Purchase #2	$148.69	8.253%	$160.9614	$160.96	$160.95	$161.00
Purchase #3	$159.35	4.104%	$165.8897	$165.89	$165.90	$165.90
Purchase #4	$61.64	7.447%	$66.2303	$66.23	$66.25	$66.20
Purchase #5	$130.78	10.292%	$144.2399	$144.24	$144.25	$144.20
Purchase #6	$250.99	12.587%	$282.5821	$282.58	$282.60	$282.60
Purchase #7	$32.31	13.217%	$36.5804	$36.58	$36.60	$36.60
7 purchase totals =	$846.29		$926.8351	$926.83	$926.90	$926.90