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	$164.79	12.546%	$185.4646	$185.46	$185.45	$185.50
Purchase #2	$152.85	12.136%	$171.3999	$171.40	$171.40	$171.40
Purchase #3	$84.92	7.748%	$91.4996	$91.50	$91.50	$91.50
Purchase #4	$94.76	10.581%	$104.7866	$104.79	$104.80	$104.80
Purchase #5	$67.77	3.195%	$69.9353	$69.94	$69.95	$69.90
Purchase #6	$78.29	12.183%	$87.8281	$87.83	$87.85	$87.80
Purchase #7	$149.47	12.397%	$167.9998	$168.00	$168.00	$168.00
7 purchase totals =	$792.85		$878.9139	$878.92	$878.95	$878.90