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	$113.54	8.527%	$123.2216	$123.22	$123.20	$123.20
Purchase #2	$129.78	5.170%	$136.4896	$136.49	$136.50	$136.50
Purchase #3	$225.49	10.606%	$249.4055	$249.41	$249.40	$249.40
Purchase #4	$65.89	9.687%	$72.2728	$72.27	$72.25	$72.30
Purchase #5	$119.27	10.595%	$131.9067	$131.91	$131.90	$131.90
Purchase #6	$144.66	7.218%	$155.1016	$155.10	$155.10	$155.10
Purchase #7	$61.85	9.590%	$67.7814	$67.78	$67.80	$67.80
7 purchase totals =	$860.48		$936.1792	$936.18	$936.15	$936.20