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	$216.31	10.717%	$239.4919	$239.49	$239.50	$239.50
Purchase #2	$52.88	5.423%	$55.7477	$55.75	$55.75	$55.70
Purchase #3	$76.88	4.426%	$80.2827	$80.28	$80.30	$80.30
Purchase #4	$215.62	6.273%	$229.1458	$229.15	$229.15	$229.10
Purchase #5	$147.55	11.350%	$164.2969	$164.30	$164.30	$164.30
Purchase #6	$92.42	11.586%	$103.1278	$103.13	$103.15	$103.10
Purchase #7	$38.38	9.744%	$42.1197	$42.12	$42.10	$42.10
7 purchase totals =	$840.04		$914.2125	$914.22	$914.25	$914.10