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	$27.76	3.455%	$28.7191	$28.72	$28.70	$28.70
Purchase #2	$138.67	10.639%	$153.4231	$153.42	$153.40	$153.40
Purchase #3	$208.93	3.811%	$216.8923	$216.89	$216.90	$216.90
Purchase #4	$113.42	8.493%	$123.0528	$123.05	$123.05	$123.10
Purchase #5	$146.61	3.684%	$152.0111	$152.01	$152.00	$152.00
Purchase #6	$23.27	7.776%	$25.0795	$25.08	$25.10	$25.10
Purchase #7	$95.46	11.736%	$106.6632	$106.66	$106.65	$106.70
7 purchase totals =	$754.12		$805.8411	$805.83	$805.80	$805.90