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	$110.69	12.449%	$124.4698	$124.47	$124.45	$124.50
Purchase #2	$203.82	11.775%	$227.8198	$227.82	$227.80	$227.80
Purchase #3	$54.80	6.700%	$58.4716	$58.47	$58.45	$58.50
Purchase #4	$144.47	10.673%	$159.8893	$159.89	$159.90	$159.90
Purchase #5	$127.72	12.591%	$143.8012	$143.80	$143.80	$143.80
Purchase #6	$14.80	7.173%	$15.8616	$15.86	$15.85	$15.90
Purchase #7	$217.63	13.276%	$246.5226	$246.52	$246.50	$246.50
7 purchase totals =	$873.93		$976.8359	$976.83	$976.75	$976.90