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	$12.70	6.299%	$13.5	$13.50	$13.50	$13.50
Purchase #2	$100.38	5.177%	$105.5767	$105.58	$105.60	$105.60
Purchase #3	$160.55	4.392%	$167.6014	$167.60	$167.60	$167.60
Purchase #4	$67.92	6.821%	$72.5528	$72.55	$72.55	$72.60
Purchase #5	$93.44	7.399%	$100.3536	$100.35	$100.35	$100.40
Purchase #6	$81.42	9.572%	$89.2135	$89.21	$89.20	$89.20
Purchase #7	$226.37	3.281%	$233.7972	$233.80	$233.80	$233.80
7 purchase totals =	$742.78		$782.5952	$782.59	$782.60	$782.70