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	$13.38	10.677%	$14.8086	$14.81	$14.80	$14.80
Purchase #2	$82.43	9.271%	$90.0721	$90.07	$90.05	$90.10
Purchase #3	$79.37	11.354%	$88.3817	$88.38	$88.40	$88.40
Purchase #4	$63.81	3.331%	$65.9355	$65.94	$65.95	$65.90
Purchase #5	$28.58	10.511%	$31.584	$31.58	$31.60	$31.60
Purchase #6	$90.69	5.656%	$95.8194	$95.82	$95.80	$95.80
Purchase #7	$201.29	13.150%	$227.7596	$227.76	$227.75	$227.80
7 purchase totals =	$559.55		$614.3609	$614.36	$614.35	$614.40