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	$100.74	3.601%	$104.3676	$104.37	$104.35	$104.40
Purchase #2	$152.67	13.212%	$172.8408	$172.84	$172.85	$172.80
Purchase #3	$150.66	10.871%	$167.0382	$167.04	$167.05	$167.00
Purchase #4	$31.40	3.109%	$32.3762	$32.38	$32.40	$32.40
Purchase #5	$217.47	10.525%	$240.3587	$240.36	$240.35	$240.40
Purchase #6	$68.62	11.341%	$76.4022	$76.40	$76.40	$76.40
Purchase #7	$116.69	13.512%	$132.4572	$132.46	$132.45	$132.50
7 purchase totals =	$838.25		$925.8409	$925.85	$925.85	$925.90