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	$97.94	11.770%	$109.4675	$109.47	$109.45	$109.50
Purchase #2	$123.85	11.482%	$138.0705	$138.07	$138.05	$138.10
Purchase #3	$60.42	4.818%	$63.331	$63.33	$63.35	$63.30
Purchase #4	$57.67	7.727%	$62.1262	$62.13	$62.15	$62.10
Purchase #5	$62.37	8.723%	$67.8105	$67.81	$67.80	$67.80
Purchase #6	$43.63	9.406%	$47.7338	$47.73	$47.75	$47.70
Purchase #7	$42.82	3.297%	$44.2318	$44.23	$44.25	$44.20
7 purchase totals =	$488.70		$532.7713	$532.77	$532.80	$532.70