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	$9.98	9.489%	$10.927	$10.93	$10.95	$10.90
Purchase #2	$86.98	3.574%	$90.0887	$90.09	$90.10	$90.10
Purchase #3	$123.36	9.478%	$135.0521	$135.05	$135.05	$135.10
Purchase #4	$158.56	8.648%	$172.2723	$172.27	$172.25	$172.30
Purchase #5	$10.62	10.766%	$11.7633	$11.76	$11.75	$11.80
Purchase #6	$119.61	7.740%	$128.8678	$128.87	$128.85	$128.90
Purchase #7	$47.87	5.323%	$50.4181	$50.42	$50.40	$50.40
7 purchase totals =	$556.98		$599.3893	$599.39	$599.35	$599.50