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	$134.36	4.102%	$139.8714	$139.87	$139.85	$139.90
Purchase #2	$60.63	9.107%	$66.1516	$66.15	$66.15	$66.20
Purchase #3	$92.37	9.225%	$100.8911	$100.89	$100.90	$100.90
Purchase #4	$141.98	6.636%	$151.4018	$151.40	$151.40	$151.40
Purchase #5	$56.35	3.163%	$58.1324	$58.13	$58.15	$58.10
Purchase #6	$155.27	3.334%	$160.4467	$160.45	$160.45	$160.40
Purchase #7	$235.33	6.463%	$250.5394	$250.54	$250.55	$250.50
7 purchase totals =	$876.29		$927.4344	$927.43	$927.45	$927.40