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	$206.72	4.164%	$215.3278	$215.33	$215.35	$215.30
Purchase #2	$50.72	8.450%	$55.0058	$55.01	$55.00	$55.00
Purchase #3	$124.57	10.477%	$137.6212	$137.62	$137.60	$137.60
Purchase #4	$11.29	10.765%	$12.5054	$12.51	$12.50	$12.50
Purchase #5	$148.86	12.772%	$167.8724	$167.87	$167.85	$167.90
Purchase #6	$54.81	10.264%	$60.4357	$60.44	$60.45	$60.40
Purchase #7	$89.85	4.204%	$93.6273	$93.63	$93.65	$93.60
7 purchase totals =	$686.82		$742.3956	$742.41	$742.40	$742.30