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	$54.43	9.164%	$59.418	$59.42	$59.40	$59.40
Purchase #2	$102.53	11.655%	$114.4799	$114.48	$114.50	$114.50
Purchase #3	$250.45	3.337%	$258.8075	$258.81	$258.80	$258.80
Purchase #4	$34.43	5.426%	$36.2982	$36.30	$36.30	$36.30
Purchase #5	$228.52	5.674%	$241.4862	$241.49	$241.50	$241.50
Purchase #6	$179.57	11.639%	$200.4702	$200.47	$200.45	$200.50
Purchase #7	$9.37	5.688%	$9.903	$9.90	$9.90	$9.90
7 purchase totals =	$859.30		$920.8630	$920.87	$920.85	$920.90