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	$125.89	10.712%	$139.3753	$139.38	$139.40	$139.40
Purchase #2	$199.48	11.677%	$222.7733	$222.77	$222.75	$222.80
Purchase #3	$69.90	4.397%	$72.9735	$72.97	$72.95	$73.00
Purchase #4	$234.64	7.593%	$252.4562	$252.46	$252.45	$252.50
Purchase #5	$31.91	4.512%	$33.3498	$33.35	$33.35	$33.30
Purchase #6	$205.63	10.583%	$227.3918	$227.39	$227.40	$227.40
Purchase #7	$122.94	13.708%	$139.7926	$139.79	$139.80	$139.80
7 purchase totals =	$990.39		$1,088.1125	$1,088.11	$1,088.10	$1,088.20