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	$92.79	8.225%	$100.422	$100.42	$100.40	$100.40
Purchase #2	$51.72	11.296%	$57.5623	$57.56	$57.55	$57.60
Purchase #3	$99.84	5.299%	$105.1305	$105.13	$105.15	$105.10
Purchase #4	$166.57	13.440%	$188.957	$188.96	$188.95	$189.00
Purchase #5	$22.46	13.533%	$25.4995	$25.50	$25.50	$25.50
Purchase #6	$47.73	5.871%	$50.5322	$50.53	$50.55	$50.50
Purchase #7	$104.53	9.409%	$114.3652	$114.37	$114.35	$114.40
7 purchase totals =	$585.64		$642.4687	$642.47	$642.45	$642.50