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	$29.68	12.799%	$33.4787	$33.48	$33.50	$33.50
Purchase #2	$157.84	4.591%	$165.0864	$165.09	$165.10	$165.10
Purchase #3	$246.53	3.497%	$255.1512	$255.15	$255.15	$255.20
Purchase #4	$132.53	4.507%	$138.5031	$138.50	$138.50	$138.50
Purchase #5	$126.66	10.125%	$139.4843	$139.48	$139.50	$139.50
Purchase #6	$35.56	9.315%	$38.8724	$38.87	$38.85	$38.90
Purchase #7	$5.36	8.577%	$5.8197	$5.82	$5.80	$5.80
7 purchase totals =	$734.16		$776.3958	$776.39	$776.40	$776.50