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	$249.28	8.147%	$269.5888	$269.59	$269.60	$269.60
Purchase #2	$95.99	9.260%	$104.8787	$104.88	$104.90	$104.90
Purchase #3	$179.51	4.580%	$187.7316	$187.73	$187.75	$187.70
Purchase #4	$65.39	3.725%	$67.8258	$67.83	$67.85	$67.80
Purchase #5	$21.84	11.306%	$24.3092	$24.31	$24.30	$24.30
Purchase #6	$208.95	12.294%	$234.6383	$234.64	$234.65	$234.60
Purchase #7	$145.45	3.528%	$150.5815	$150.58	$150.60	$150.60
7 purchase totals =	$966.41		$1,039.5539	$1,039.56	$1,039.65	$1,039.50