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	$74.37	10.826%	$82.4213	$82.42	$82.40	$82.40
Purchase #2	$82.74	8.601%	$89.8565	$89.86	$89.85	$89.90
Purchase #3	$191.38	6.271%	$203.3814	$203.38	$203.40	$203.40
Purchase #4	$70.41	5.277%	$74.1255	$74.13	$74.15	$74.10
Purchase #5	$149.94	12.417%	$168.558	$168.56	$168.55	$168.60
Purchase #6	$103.41	12.630%	$116.4707	$116.47	$116.45	$116.50
Purchase #7	$55.96	12.520%	$62.9662	$62.97	$62.95	$63.00
7 purchase totals =	$728.21		$797.7796	$797.79	$797.75	$797.90