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	$219.77	13.870%	$250.2521	$250.25	$250.25	$250.30
Purchase #2	$40.40	3.848%	$41.9546	$41.95	$41.95	$42.00
Purchase #3	$189.94	12.482%	$213.6483	$213.65	$213.65	$213.60
Purchase #4	$90.42	11.614%	$100.9214	$100.92	$100.90	$100.90
Purchase #5	$87.38	5.655%	$92.3213	$92.32	$92.30	$92.30
Purchase #6	$31.35	3.663%	$32.4984	$32.50	$32.50	$32.50
Purchase #7	$160.76	10.670%	$177.9131	$177.91	$177.90	$177.90
7 purchase totals =	$820.02		$909.5092	$909.50	$909.45	$909.50