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	$105.38	12.286%	$118.327	$118.33	$118.35	$118.30
Purchase #2	$242.77	12.818%	$273.8883	$273.89	$273.90	$273.90
Purchase #3	$68.33	6.186%	$72.5569	$72.56	$72.55	$72.60
Purchase #4	$147.42	10.835%	$163.393	$163.39	$163.40	$163.40
Purchase #5	$29.50	8.721%	$32.0727	$32.07	$32.05	$32.10
Purchase #6	$16.33	13.693%	$18.5661	$18.57	$18.55	$18.60
Purchase #7	$103.45	4.279%	$107.8766	$107.88	$107.90	$107.90
7 purchase totals =	$713.18		$786.6806	$786.69	$786.70	$786.80