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	$29.67	5.862%	$31.4093	$31.41	$31.40	$31.40
Purchase #2	$76.77	4.712%	$80.3874	$80.39	$80.40	$80.40
Purchase #3	$49.32	9.522%	$54.0163	$54.02	$54.00	$54.00
Purchase #4	$66.99	5.788%	$70.8674	$70.87	$70.85	$70.90
Purchase #5	$111.32	5.609%	$117.5639	$117.56	$117.55	$117.60
Purchase #6	$226.56	12.337%	$254.5107	$254.51	$254.50	$254.50
Purchase #7	$199.76	3.187%	$206.1264	$206.13	$206.15	$206.10
7 purchase totals =	$760.39		$814.8814	$814.89	$814.85	$814.90