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	$110.91	9.264%	$121.1847	$121.18	$121.20	$121.20
Purchase #2	$37.83	12.545%	$42.5758	$42.58	$42.60	$42.60
Purchase #3	$82.86	10.724%	$91.7459	$91.75	$91.75	$91.70
Purchase #4	$160.97	4.732%	$168.5871	$168.59	$168.60	$168.60
Purchase #5	$70.69	5.397%	$74.5051	$74.51	$74.50	$74.50
Purchase #6	$141.79	4.617%	$148.3364	$148.34	$148.35	$148.30
Purchase #7	$205.90	10.401%	$227.3157	$227.32	$227.30	$227.30
7 purchase totals =	$810.95		$874.2507	$874.27	$874.30	$874.20