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	$122.96	11.318%	$136.8766	$136.88	$136.90	$136.90
Purchase #2	$33.32	6.550%	$35.5025	$35.50	$35.50	$35.50
Purchase #3	$239.83	12.426%	$269.6313	$269.63	$269.65	$269.60
Purchase #4	$66.99	7.632%	$72.1027	$72.10	$72.10	$72.10
Purchase #5	$17.27	11.492%	$19.2547	$19.25	$19.25	$19.30
Purchase #6	$30.34	13.735%	$34.5072	$34.51	$34.50	$34.50
Purchase #7	$88.42	13.196%	$100.0879	$100.09	$100.10	$100.10
7 purchase totals =	$599.13		$667.9629	$667.96	$668.00	$668.00