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	$50.42	4.739%	$52.8094	$52.81	$52.80	$52.80
Purchase #2	$240.91	12.721%	$271.5562	$271.56	$271.55	$271.60
Purchase #3	$20.51	3.592%	$21.2467	$21.25	$21.25	$21.20
Purchase #4	$95.88	6.510%	$102.1218	$102.12	$102.10	$102.10
Purchase #5	$168.96	6.480%	$179.9086	$179.91	$179.90	$179.90
Purchase #6	$95.42	5.776%	$100.9315	$100.93	$100.95	$100.90
Purchase #7	$114.61	5.517%	$120.933	$120.93	$120.95	$120.90
7 purchase totals =	$786.71		$849.5072	$849.51	$849.50	$849.40