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	$104.93	6.664%	$111.9225	$111.92	$111.90	$111.90
Purchase #2	$83.86	8.106%	$90.6577	$90.66	$90.65	$90.70
Purchase #3	$112.64	4.126%	$117.2875	$117.29	$117.30	$117.30
Purchase #4	$29.93	7.753%	$32.2505	$32.25	$32.25	$32.30
Purchase #5	$195.41	11.859%	$218.5837	$218.58	$218.60	$218.60
Purchase #6	$177.63	10.309%	$195.9419	$195.94	$195.95	$195.90
Purchase #7	$219.81	11.579%	$245.2618	$245.26	$245.25	$245.30
7 purchase totals =	$924.21		$1,011.9056	$1,011.90	$1,011.90	$1,012.00