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	$134.69	11.414%	$150.0635	$150.06	$150.05	$150.10
Purchase #2	$140.56	7.309%	$150.8335	$150.83	$150.85	$150.80
Purchase #3	$174.81	10.130%	$192.5183	$192.52	$192.50	$192.50
Purchase #4	$194.39	5.162%	$204.4244	$204.42	$204.40	$204.40
Purchase #5	$196.96	3.272%	$203.4045	$203.40	$203.40	$203.40
Purchase #6	$36.78	4.801%	$38.5458	$38.55	$38.55	$38.50
Purchase #7	$75.81	5.641%	$80.0864	$80.09	$80.10	$80.10
7 purchase totals =	$954.00		$1,019.8764	$1,019.87	$1,019.85	$1,019.80