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	$47.80	5.607%	$50.4801	$50.48	$50.50	$50.50
Purchase #2	$169.45	4.309%	$176.7516	$176.75	$176.75	$176.80
Purchase #3	$95.57	6.198%	$101.4934	$101.49	$101.50	$101.50
Purchase #4	$143.55	11.731%	$160.3899	$160.39	$160.40	$160.40
Purchase #5	$56.59	10.666%	$62.6259	$62.63	$62.65	$62.60
Purchase #6	$72.25	11.379%	$80.4713	$80.47	$80.45	$80.50
Purchase #7	$190.35	5.140%	$200.134	$200.13	$200.15	$200.10
7 purchase totals =	$775.56		$832.3462	$832.34	$832.40	$832.40