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	$42.95	4.551%	$44.9047	$44.90	$44.90	$44.90
Purchase #2	$234.25	3.464%	$242.3644	$242.36	$242.35	$242.40
Purchase #3	$54.40	9.148%	$59.3765	$59.38	$59.40	$59.40
Purchase #4	$109.59	9.131%	$119.5967	$119.60	$119.60	$119.60
Purchase #5	$112.66	4.569%	$117.8074	$117.81	$117.80	$117.80
Purchase #6	$22.55	7.533%	$24.2487	$24.25	$24.25	$24.20
Purchase #7	$48.86	13.251%	$55.3344	$55.33	$55.35	$55.30
7 purchase totals =	$625.26		$663.6328	$663.63	$663.65	$663.60