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	$99.66	12.667%	$112.2839	$112.28	$112.30	$112.30
Purchase #2	$29.95	6.422%	$31.8734	$31.87	$31.85	$31.90
Purchase #3	$167.33	12.637%	$188.4755	$188.48	$188.50	$188.50
Purchase #4	$107.46	4.177%	$111.9486	$111.95	$111.95	$111.90
Purchase #5	$102.69	4.198%	$107.0009	$107.00	$107.00	$107.00
Purchase #6	$30.53	9.254%	$33.3552	$33.36	$33.35	$33.40
Purchase #7	$80.32	12.614%	$90.4516	$90.45	$90.45	$90.50
7 purchase totals =	$617.94		$675.3891	$675.39	$675.40	$675.50