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	$12.51	8.571%	$13.5822	$13.58	$13.60	$13.60
Purchase #2	$144.83	9.273%	$158.2601	$158.26	$158.25	$158.30
Purchase #3	$63.31	6.485%	$67.4157	$67.42	$67.40	$67.40
Purchase #4	$126.90	13.732%	$144.3259	$144.33	$144.35	$144.30
Purchase #5	$150.57	9.256%	$164.5068	$164.51	$164.50	$164.50
Purchase #6	$245.63	7.712%	$264.573	$264.57	$264.55	$264.60
Purchase #7	$29.90	8.159%	$32.3395	$32.34	$32.35	$32.30
7 purchase totals =	$773.65		$845.0032	$845.01	$845.00	$845.00