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	$240.61	12.126%	$269.7864	$269.79	$269.80	$269.80
Purchase #2	$61.94	8.240%	$67.0439	$67.04	$67.05	$67.00
Purchase #3	$84.72	11.845%	$94.7551	$94.76	$94.75	$94.80
Purchase #4	$20.90	7.389%	$22.4443	$22.44	$22.45	$22.40
Purchase #5	$72.75	8.305%	$78.7919	$78.79	$78.80	$78.80
Purchase #6	$19.34	5.607%	$20.4244	$20.42	$20.40	$20.40
Purchase #7	$97.27	3.511%	$100.6851	$100.69	$100.70	$100.70
7 purchase totals =	$597.53		$653.9311	$653.93	$653.95	$653.90