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	$38.66	4.729%	$40.4882	$40.49	$40.50	$40.50
Purchase #2	$102.51	9.297%	$112.0404	$112.04	$112.05	$112.00
Purchase #3	$107.46	11.299%	$119.6019	$119.60	$119.60	$119.60
Purchase #4	$159.74	4.124%	$166.3277	$166.33	$166.35	$166.30
Purchase #5	$227.62	4.808%	$238.564	$238.56	$238.55	$238.60
Purchase #6	$118.76	9.145%	$129.6206	$129.62	$129.60	$129.60
Purchase #7	$47.49	13.208%	$53.7625	$53.76	$53.75	$53.80
7 purchase totals =	$802.24		$860.4053	$860.40	$860.40	$860.40