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	$104.26	3.200%	$107.5963	$107.60	$107.60	$107.60
Purchase #2	$210.98	12.350%	$237.036	$237.04	$237.05	$237.00
Purchase #3	$68.89	7.184%	$73.8391	$73.84	$73.85	$73.80
Purchase #4	$114.86	10.722%	$127.1753	$127.18	$127.20	$127.20
Purchase #5	$52.90	3.754%	$54.8859	$54.89	$54.90	$54.90
Purchase #6	$152.82	6.580%	$162.8756	$162.88	$162.90	$162.90
Purchase #7	$50.55	8.557%	$54.8756	$54.88	$54.90	$54.90
7 purchase totals =	$755.26		$818.2838	$818.31	$818.40	$818.30