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	$55.96	6.822%	$59.7776	$59.78	$59.80	$59.80
Purchase #2	$151.40	8.424%	$164.1539	$164.15	$164.15	$164.20
Purchase #3	$202.76	7.255%	$217.4702	$217.47	$217.45	$217.50
Purchase #4	$110.35	3.495%	$114.2067	$114.21	$114.20	$114.20
Purchase #5	$99.71	5.468%	$105.1621	$105.16	$105.15	$105.20
Purchase #6	$179.66	8.445%	$194.8323	$194.83	$194.85	$194.80
Purchase #7	$14.42	7.721%	$15.5334	$15.53	$15.55	$15.50
7 purchase totals =	$814.26		$871.1362	$871.13	$871.15	$871.20