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	$239.35	12.188%	$268.522	$268.52	$268.50	$268.50
Purchase #2	$200.52	5.167%	$210.8809	$210.88	$210.90	$210.90
Purchase #3	$143.96	9.796%	$158.0623	$158.06	$158.05	$158.10
Purchase #4	$208.39	4.297%	$217.3445	$217.34	$217.35	$217.30
Purchase #5	$110.27	3.466%	$114.092	$114.09	$114.10	$114.10
Purchase #6	$29.87	7.658%	$32.1574	$32.16	$32.15	$32.20
Purchase #7	$166.88	12.811%	$188.259	$188.26	$188.25	$188.30
7 purchase totals =	$1,099.24		$1,189.3181	$1,189.31	$1,189.30	$1,189.40