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	$36.71	5.475%	$38.7199	$38.72	$38.70	$38.70
Purchase #2	$217.87	4.427%	$227.5151	$227.52	$227.50	$227.50
Purchase #3	$125.76	12.521%	$141.5064	$141.51	$141.50	$141.50
Purchase #4	$44.44	13.834%	$50.5878	$50.59	$50.60	$50.60
Purchase #5	$175.96	10.584%	$194.5836	$194.58	$194.60	$194.60
Purchase #6	$40.78	6.123%	$43.277	$43.28	$43.30	$43.30
Purchase #7	$202.95	7.592%	$218.358	$218.36	$218.35	$218.40
7 purchase totals =	$844.47		$914.5478	$914.56	$914.55	$914.60