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	$100.72	10.691%	$111.488	$111.49	$111.50	$111.50
Purchase #2	$165.63	10.277%	$182.6518	$182.65	$182.65	$182.70
Purchase #3	$208.54	5.179%	$219.3403	$219.34	$219.35	$219.30
Purchase #4	$95.67	3.520%	$99.0376	$99.04	$99.05	$99.00
Purchase #5	$49.47	7.601%	$53.2302	$53.23	$53.25	$53.20
Purchase #6	$187.52	11.499%	$209.0829	$209.08	$209.10	$209.10
Purchase #7	$13.86	12.130%	$15.5412	$15.54	$15.55	$15.50
7 purchase totals =	$821.41		$890.3720	$890.37	$890.45	$890.30