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	$89.99	11.659%	$100.4819	$100.48	$100.50	$100.50
Purchase #2	$226.47	9.198%	$247.3007	$247.30	$247.30	$247.30
Purchase #3	$131.80	7.743%	$142.0053	$142.01	$142.00	$142.00
Purchase #4	$24.57	11.611%	$27.4228	$27.42	$27.40	$27.40
Purchase #5	$151.86	10.368%	$167.6048	$167.60	$167.60	$167.60
Purchase #6	$7.90	11.452%	$8.8047	$8.80	$8.80	$8.80
Purchase #7	$50.49	12.682%	$56.8931	$56.89	$56.90	$56.90
7 purchase totals =	$683.08		$750.5133	$750.50	$750.50	$750.50