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	$29.26	12.627%	$32.9547	$32.95	$32.95	$33.00
Purchase #2	$41.61	13.233%	$47.1163	$47.12	$47.10	$47.10
Purchase #3	$61.26	10.808%	$67.881	$67.88	$67.90	$67.90
Purchase #4	$216.48	11.802%	$242.029	$242.03	$242.05	$242.00
Purchase #5	$123.39	10.764%	$136.6717	$136.67	$136.65	$136.70
Purchase #6	$35.98	7.694%	$38.7483	$38.75	$38.75	$38.70
Purchase #7	$74.65	5.683%	$78.8924	$78.89	$78.90	$78.90
7 purchase totals =	$582.63		$644.2934	$644.29	$644.30	$644.30