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	$41.53	13.180%	$47.0037	$47.00	$47.00	$47.00
Purchase #2	$203.72	10.105%	$224.3059	$224.31	$224.30	$224.30
Purchase #3	$53.96	9.668%	$59.1769	$59.18	$59.20	$59.20
Purchase #4	$25.29	13.856%	$28.7942	$28.79	$28.80	$28.80
Purchase #5	$126.34	4.139%	$131.5692	$131.57	$131.55	$131.60
Purchase #6	$158.67	12.512%	$178.5228	$178.52	$178.50	$178.50
Purchase #7	$155.50	13.308%	$176.1939	$176.19	$176.20	$176.20
7 purchase totals =	$765.01		$845.5666	$845.56	$845.55	$845.60