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	$95.35	5.234%	$100.3406	$100.34	$100.35	$100.30
Purchase #2	$120.54	3.363%	$124.5938	$124.59	$124.60	$124.60
Purchase #3	$182.34	6.573%	$194.3252	$194.33	$194.35	$194.30
Purchase #4	$132.81	5.492%	$140.1039	$140.10	$140.10	$140.10
Purchase #5	$10.79	9.309%	$11.7944	$11.79	$11.80	$11.80
Purchase #6	$146.53	6.365%	$155.8566	$155.86	$155.85	$155.90
Purchase #7	$72.51	12.455%	$81.5411	$81.54	$81.55	$81.50
7 purchase totals =	$760.87		$808.5556	$808.55	$808.60	$808.50