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	$142.73	6.778%	$152.4042	$152.40	$152.40	$152.40
Purchase #2	$91.45	12.830%	$103.183	$103.18	$103.20	$103.20
Purchase #3	$247.76	7.577%	$266.5328	$266.53	$266.55	$266.50
Purchase #4	$164.47	13.650%	$186.9202	$186.92	$186.90	$186.90
Purchase #5	$243.69	5.665%	$257.495	$257.50	$257.50	$257.50
Purchase #6	$95.91	3.851%	$99.6035	$99.60	$99.60	$99.60
Purchase #7	$69.63	6.780%	$74.3509	$74.35	$74.35	$74.40
7 purchase totals =	$1,055.64		$1,140.4896	$1,140.48	$1,140.50	$1,140.50