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	$250.91	11.623%	$280.0733	$280.07	$280.05	$280.10
Purchase #2	$231.61	6.369%	$246.3612	$246.36	$246.35	$246.40
Purchase #3	$67.89	7.176%	$72.7618	$72.76	$72.75	$72.80
Purchase #4	$156.93	5.152%	$165.015	$165.02	$165.00	$165.00
Purchase #5	$247.69	5.206%	$260.5847	$260.58	$260.60	$260.60
Purchase #6	$129.76	11.395%	$144.5462	$144.55	$144.55	$144.50
Purchase #7	$233.59	9.575%	$255.9562	$255.96	$255.95	$256.00
7 purchase totals =	$1,318.38		$1,425.2984	$1,425.30	$1,425.25	$1,425.40