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	$47.92	3.864%	$49.7716	$49.77	$49.75	$49.80
Purchase #2	$32.57	4.531%	$34.0457	$34.05	$34.05	$34.00
Purchase #3	$143.41	6.266%	$152.3961	$152.40	$152.40	$152.40
Purchase #4	$80.48	7.561%	$86.5651	$86.57	$86.55	$86.60
Purchase #5	$117.28	5.248%	$123.4349	$123.43	$123.45	$123.40
Purchase #6	$35.69	5.822%	$37.7679	$37.77	$37.75	$37.80
Purchase #7	$174.55	6.477%	$185.8556	$185.86	$185.85	$185.90
7 purchase totals =	$631.90		$669.8369	$669.85	$669.80	$669.90