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	$242.44	12.670%	$273.1571	$273.16	$273.15	$273.20
Purchase #2	$112.70	13.491%	$127.9044	$127.90	$127.90	$127.90
Purchase #3	$142.48	11.663%	$159.0974	$159.10	$159.10	$159.10
Purchase #4	$246.61	3.834%	$256.065	$256.07	$256.05	$256.10
Purchase #5	$136.82	6.214%	$145.322	$145.32	$145.30	$145.30
Purchase #6	$177.51	7.801%	$191.3576	$191.36	$191.35	$191.40
Purchase #7	$26.42	4.474%	$27.602	$27.60	$27.60	$27.60
7 purchase totals =	$1,084.98		$1,180.5055	$1,180.51	$1,180.45	$1,180.60