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	$69.77	12.126%	$78.2303	$78.23	$78.25	$78.20
Purchase #2	$68.93	5.339%	$72.6102	$72.61	$72.60	$72.60
Purchase #3	$218.89	4.527%	$228.7992	$228.80	$228.80	$228.80
Purchase #4	$80.95	8.706%	$87.9975	$88.00	$88.00	$88.00
Purchase #5	$236.26	10.818%	$261.8186	$261.82	$261.80	$261.80
Purchase #6	$86.55	5.667%	$91.4548	$91.45	$91.45	$91.50
Purchase #7	$141.53	7.490%	$152.1306	$152.13	$152.15	$152.10
7 purchase totals =	$902.88		$973.0412	$973.04	$973.05	$973.00