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	$92.90	11.474%	$103.5593	$103.56	$103.55	$103.60
Purchase #2	$73.70	8.591%	$80.0316	$80.03	$80.05	$80.00
Purchase #3	$19.79	6.780%	$21.1318	$21.13	$21.15	$21.10
Purchase #4	$65.31	3.277%	$67.4502	$67.45	$67.45	$67.50
Purchase #5	$222.82	10.703%	$246.6684	$246.67	$246.65	$246.70
Purchase #6	$81.65	10.676%	$90.367	$90.37	$90.35	$90.40
Purchase #7	$30.31	6.487%	$32.2762	$32.28	$32.30	$32.30
7 purchase totals =	$586.48		$641.4845	$641.49	$641.50	$641.60