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	$109.26	7.262%	$117.1945	$117.19	$117.20	$117.20
Purchase #2	$207.25	7.854%	$223.5274	$223.53	$223.55	$223.50
Purchase #3	$202.71	3.147%	$209.0893	$209.09	$209.10	$209.10
Purchase #4	$115.42	10.484%	$127.5206	$127.52	$127.50	$127.50
Purchase #5	$183.25	4.509%	$191.5127	$191.51	$191.50	$191.50
Purchase #6	$25.50	6.502%	$27.158	$27.16	$27.15	$27.20
Purchase #7	$27.37	6.439%	$29.1324	$29.13	$29.15	$29.10
7 purchase totals =	$870.76		$925.1349	$925.13	$925.15	$925.10