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	$54.43	10.132%	$59.9448	$59.94	$59.95	$59.90
Purchase #2	$174.36	3.467%	$180.4051	$180.41	$180.40	$180.40
Purchase #3	$235.55	8.517%	$255.6118	$255.61	$255.60	$255.60
Purchase #4	$143.78	11.314%	$160.0473	$160.05	$160.05	$160.00
Purchase #5	$38.34	11.650%	$42.8066	$42.81	$42.80	$42.80
Purchase #6	$189.49	5.464%	$199.8437	$199.84	$199.85	$199.80
Purchase #7	$122.61	12.186%	$137.5513	$137.55	$137.55	$137.60
7 purchase totals =	$958.56		$1,036.2106	$1,036.21	$1,036.20	$1,036.10