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	$168.31	6.624%	$179.4589	$179.46	$179.45	$179.50
Purchase #2	$20.70	13.242%	$23.4411	$23.44	$23.45	$23.40
Purchase #3	$152.81	12.291%	$171.5919	$171.59	$171.60	$171.60
Purchase #4	$244.28	10.220%	$269.2454	$269.25	$269.25	$269.20
Purchase #5	$123.62	11.554%	$137.9031	$137.90	$137.90	$137.90
Purchase #6	$221.73	12.483%	$249.4086	$249.41	$249.40	$249.40
Purchase #7	$107.96	6.102%	$114.5477	$114.55	$114.55	$114.50
7 purchase totals =	$1,039.41		$1,145.5967	$1,145.60	$1,145.60	$1,145.50