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	$90.67	10.854%	$100.5113	$100.51	$100.50	$100.50
Purchase #2	$60.30	12.585%	$67.8888	$67.89	$67.90	$67.90
Purchase #3	$58.55	3.137%	$60.3867	$60.39	$60.40	$60.40
Purchase #4	$175.81	12.351%	$197.5243	$197.52	$197.50	$197.50
Purchase #5	$185.62	13.631%	$210.9219	$210.92	$210.90	$210.90
Purchase #6	$198.31	9.199%	$216.5525	$216.55	$216.55	$216.60
Purchase #7	$14.63	6.192%	$15.5359	$15.54	$15.55	$15.50
7 purchase totals =	$783.89		$869.3214	$869.32	$869.30	$869.30