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	$139.56	7.314%	$149.7674	$149.77	$149.75	$149.80
Purchase #2	$73.45	11.684%	$82.0319	$82.03	$82.05	$82.00
Purchase #3	$40.92	4.562%	$42.7868	$42.79	$42.80	$42.80
Purchase #4	$115.53	13.736%	$131.3992	$131.40	$131.40	$131.40
Purchase #5	$67.49	3.758%	$70.0263	$70.03	$70.05	$70.00
Purchase #6	$83.32	4.367%	$86.9586	$86.96	$86.95	$87.00
Purchase #7	$59.80	11.123%	$66.4516	$66.45	$66.45	$66.50
7 purchase totals =	$580.07		$629.4218	$629.43	$629.45	$629.50