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	$148.66	7.369%	$159.6148	$159.61	$159.60	$159.60
Purchase #2	$219.88	8.514%	$238.6006	$238.60	$238.60	$238.60
Purchase #3	$200.64	13.336%	$227.3974	$227.40	$227.40	$227.40
Purchase #4	$199.56	9.229%	$217.9774	$217.98	$218.00	$218.00
Purchase #5	$33.87	11.239%	$37.6766	$37.68	$37.70	$37.70
Purchase #6	$30.47	3.402%	$31.5066	$31.51	$31.50	$31.50
Purchase #7	$219.82	10.732%	$243.4111	$243.41	$243.40	$243.40
7 purchase totals =	$1,052.90		$1,156.1845	$1,156.19	$1,156.20	$1,156.20