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	$30.35	6.368%	$32.2827	$32.28	$32.30	$32.30
Purchase #2	$235.58	13.295%	$266.9004	$266.90	$266.90	$266.90
Purchase #3	$135.58	3.608%	$140.4717	$140.47	$140.45	$140.50
Purchase #4	$65.86	7.815%	$71.007	$71.01	$71.00	$71.00
Purchase #5	$20.31	11.272%	$22.5993	$22.60	$22.60	$22.60
Purchase #6	$55.77	6.725%	$59.5205	$59.52	$59.50	$59.50
Purchase #7	$34.42	4.843%	$36.087	$36.09	$36.10	$36.10
7 purchase totals =	$577.87		$628.8686	$628.87	$628.85	$628.90