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	$128.57	7.797%	$138.5946	$138.59	$138.60	$138.60
Purchase #2	$138.97	11.457%	$154.8918	$154.89	$154.90	$154.90
Purchase #3	$132.91	3.410%	$137.4422	$137.44	$137.45	$137.40
Purchase #4	$198.46	3.718%	$205.8387	$205.84	$205.85	$205.80
Purchase #5	$165.71	8.128%	$179.1789	$179.18	$179.20	$179.20
Purchase #6	$178.70	8.595%	$194.0593	$194.06	$194.05	$194.10
Purchase #7	$72.88	13.157%	$82.4688	$82.47	$82.45	$82.50
7 purchase totals =	$1,016.20		$1,092.4743	$1,092.47	$1,092.50	$1,092.50