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	$65.96	3.803%	$68.4685	$68.47	$68.45	$68.50
Purchase #2	$128.38	13.579%	$145.8127	$145.81	$145.80	$145.80
Purchase #3	$130.89	7.762%	$141.0497	$141.05	$141.05	$141.00
Purchase #4	$248.35	12.787%	$280.1065	$280.11	$280.10	$280.10
Purchase #5	$53.25	7.273%	$57.1229	$57.12	$57.10	$57.10
Purchase #6	$160.35	5.316%	$168.8742	$168.87	$168.85	$168.90
Purchase #7	$33.76	11.441%	$37.6225	$37.62	$37.60	$37.60
7 purchase totals =	$820.94		$899.0570	$899.05	$898.95	$899.00