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	$69.77	8.665%	$75.8156	$75.82	$75.80	$75.80
Purchase #2	$184.68	8.219%	$199.8588	$199.86	$199.85	$199.90
Purchase #3	$115.34	11.477%	$128.5776	$128.58	$128.60	$128.60
Purchase #4	$181.32	8.326%	$196.4167	$196.42	$196.40	$196.40
Purchase #5	$34.62	3.674%	$35.8919	$35.89	$35.90	$35.90
Purchase #6	$183.90	3.865%	$191.0077	$191.01	$191.00	$191.00
Purchase #7	$103.99	7.162%	$111.4378	$111.44	$111.45	$111.40
7 purchase totals =	$873.62		$939.0061	$939.02	$939.00	$939.00