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	$15.81	10.634%	$17.4912	$17.49	$17.50	$17.50
Purchase #2	$33.82	10.795%	$37.4709	$37.47	$37.45	$37.50
Purchase #3	$75.63	13.601%	$85.9164	$85.92	$85.90	$85.90
Purchase #4	$82.65	6.595%	$88.1008	$88.10	$88.10	$88.10
Purchase #5	$168.32	8.645%	$182.8713	$182.87	$182.85	$182.90
Purchase #6	$166.44	10.762%	$184.3523	$184.35	$184.35	$184.40
Purchase #7	$47.95	13.662%	$54.5009	$54.50	$54.50	$54.50
7 purchase totals =	$590.62		$650.7038	$650.70	$650.65	$650.80