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	$112.48	9.817%	$123.5222	$123.52	$123.50	$123.50
Purchase #2	$84.82	11.792%	$94.822	$94.82	$94.80	$94.80
Purchase #3	$54.45	4.368%	$56.8284	$56.83	$56.85	$56.80
Purchase #4	$30.44	3.691%	$31.5635	$31.56	$31.55	$31.60
Purchase #5	$222.29	12.697%	$250.5142	$250.51	$250.50	$250.50
Purchase #6	$17.87	13.759%	$20.3287	$20.33	$20.35	$20.30
Purchase #7	$152.26	12.780%	$171.7188	$171.72	$171.70	$171.70
7 purchase totals =	$674.61		$749.2978	$749.29	$749.25	$749.20