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	$19.94	4.762%	$20.8895	$20.89	$20.90	$20.90
Purchase #2	$137.73	7.741%	$148.3917	$148.39	$148.40	$148.40
Purchase #3	$168.27	8.605%	$182.7496	$182.75	$182.75	$182.70
Purchase #4	$246.98	5.631%	$260.8874	$260.89	$260.90	$260.90
Purchase #5	$94.82	4.742%	$99.3164	$99.32	$99.30	$99.30
Purchase #6	$204.80	10.542%	$226.39	$226.39	$226.40	$226.40
Purchase #7	$13.93	13.270%	$15.7785	$15.78	$15.80	$15.80
7 purchase totals =	$886.47		$954.4031	$954.41	$954.45	$954.40