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	$213.33	13.631%	$242.409	$242.41	$242.40	$242.40
Purchase #2	$176.94	11.305%	$196.9431	$196.94	$196.95	$196.90
Purchase #3	$208.80	10.842%	$231.4381	$231.44	$231.45	$231.40
Purchase #4	$183.43	7.170%	$196.5819	$196.58	$196.60	$196.60
Purchase #5	$207.29	7.480%	$222.7953	$222.80	$222.80	$222.80
Purchase #6	$7.99	3.837%	$8.2966	$8.30	$8.30	$8.30
Purchase #7	$109.68	12.342%	$123.2167	$123.22	$123.20	$123.20
7 purchase totals =	$1,107.46		$1,221.6807	$1,221.69	$1,221.70	$1,221.60