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	$20.81	3.746%	$21.5895	$21.59	$21.60	$21.60
Purchase #2	$111.66	13.343%	$126.5588	$126.56	$126.55	$126.60
Purchase #3	$166.77	10.870%	$184.8979	$184.90	$184.90	$184.90
Purchase #4	$186.30	6.362%	$198.1524	$198.15	$198.15	$198.20
Purchase #5	$105.83	3.432%	$109.4621	$109.46	$109.45	$109.50
Purchase #6	$171.70	12.197%	$192.6422	$192.64	$192.65	$192.60
Purchase #7	$161.38	9.220%	$176.2592	$176.26	$176.25	$176.30
7 purchase totals =	$924.45		$1,009.5621	$1,009.56	$1,009.55	$1,009.70