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	$139.54	11.501%	$155.5885	$155.59	$155.60	$155.60
Purchase #2	$131.30	10.109%	$144.5731	$144.57	$144.55	$144.60
Purchase #3	$95.97	9.547%	$105.1323	$105.13	$105.15	$105.10
Purchase #4	$131.84	5.547%	$139.1532	$139.15	$139.15	$139.20
Purchase #5	$141.37	12.427%	$158.938	$158.94	$158.95	$158.90
Purchase #6	$97.40	9.669%	$106.8176	$106.82	$106.80	$106.80
Purchase #7	$104.72	5.813%	$110.8074	$110.81	$110.80	$110.80
7 purchase totals =	$842.14		$921.0101	$921.01	$921.00	$921.00