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	$29.95	7.198%	$32.1058	$32.11	$32.10	$32.10
Purchase #2	$136.26	4.246%	$142.0456	$142.05	$142.05	$142.00
Purchase #3	$147.53	5.861%	$156.1767	$156.18	$156.20	$156.20
Purchase #4	$163.70	5.587%	$172.8459	$172.85	$172.85	$172.80
Purchase #5	$155.25	6.252%	$164.9562	$164.96	$164.95	$165.00
Purchase #6	$53.38	7.864%	$57.5778	$57.58	$57.60	$57.60
Purchase #7	$161.79	6.208%	$171.8339	$171.83	$171.85	$171.80
7 purchase totals =	$847.86		$897.5419	$897.56	$897.60	$897.50