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	$18.71	9.434%	$20.4751	$20.48	$20.50	$20.50
Purchase #2	$166.55	3.605%	$172.5541	$172.55	$172.55	$172.60
Purchase #3	$231.38	3.573%	$239.6472	$239.65	$239.65	$239.60
Purchase #4	$40.89	8.620%	$44.4147	$44.41	$44.40	$44.40
Purchase #5	$220.55	12.629%	$248.4033	$248.40	$248.40	$248.40
Purchase #6	$238.72	8.174%	$258.233	$258.23	$258.25	$258.20
Purchase #7	$59.75	6.111%	$63.4013	$63.40	$63.40	$63.40
7 purchase totals =	$976.55		$1,047.1287	$1,047.12	$1,047.15	$1,047.10