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	$233.34	8.636%	$253.4912	$253.49	$253.50	$253.50
Purchase #2	$86.50	10.309%	$95.4173	$95.42	$95.40	$95.40
Purchase #3	$162.94	7.566%	$175.268	$175.27	$175.25	$175.30
Purchase #4	$8.29	12.625%	$9.3366	$9.34	$9.35	$9.30
Purchase #5	$67.85	6.677%	$72.3803	$72.38	$72.40	$72.40
Purchase #6	$187.94	12.516%	$211.4626	$211.46	$211.45	$211.50
Purchase #7	$27.94	5.694%	$29.5309	$29.53	$29.55	$29.50
7 purchase totals =	$774.80		$846.8869	$846.89	$846.90	$846.90