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	$55.54	11.457%	$61.9032	$61.90	$61.90	$61.90
Purchase #2	$36.32	10.663%	$40.1928	$40.19	$40.20	$40.20
Purchase #3	$240.35	13.737%	$273.3669	$273.37	$273.35	$273.40
Purchase #4	$47.43	13.574%	$53.8681	$53.87	$53.85	$53.90
Purchase #5	$75.87	10.637%	$83.9403	$83.94	$83.95	$83.90
Purchase #6	$155.48	6.800%	$166.0526	$166.05	$166.05	$166.10
Purchase #7	$52.29	6.727%	$55.8075	$55.81	$55.80	$55.80
7 purchase totals =	$663.28		$735.1314	$735.13	$735.10	$735.20