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	$101.49	9.744%	$111.3792	$111.38	$111.40	$111.40
Purchase #2	$245.71	10.869%	$272.4162	$272.42	$272.40	$272.40
Purchase #3	$77.42	7.499%	$83.2257	$83.23	$83.25	$83.20
Purchase #4	$154.88	10.278%	$170.7986	$170.80	$170.80	$170.80
Purchase #5	$109.69	6.513%	$116.8341	$116.83	$116.85	$116.80
Purchase #6	$172.85	8.422%	$187.4074	$187.41	$187.40	$187.40
Purchase #7	$210.78	3.551%	$218.2648	$218.26	$218.25	$218.30
7 purchase totals =	$1,072.82		$1,160.3260	$1,160.33	$1,160.35	$1,160.30