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	$101.84	10.369%	$112.3998	$112.40	$112.40	$112.40
Purchase #2	$66.66	9.320%	$72.8727	$72.87	$72.85	$72.90
Purchase #3	$109.61	13.717%	$124.6452	$124.65	$124.65	$124.60
Purchase #4	$98.33	9.840%	$108.0057	$108.01	$108.00	$108.00
Purchase #5	$144.29	8.329%	$156.3079	$156.31	$156.30	$156.30
Purchase #6	$54.87	11.622%	$61.247	$61.25	$61.25	$61.20
Purchase #7	$12.32	3.224%	$12.7172	$12.72	$12.70	$12.70
7 purchase totals =	$587.92		$648.1955	$648.21	$648.15	$648.10