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	$144.46	6.351%	$153.6347	$153.63	$153.65	$153.60
Purchase #2	$34.95	10.528%	$38.6295	$38.63	$38.65	$38.60
Purchase #3	$40.31	13.700%	$45.8325	$45.83	$45.85	$45.80
Purchase #4	$162.80	4.635%	$170.3458	$170.35	$170.35	$170.30
Purchase #5	$19.88	8.114%	$21.4931	$21.49	$21.50	$21.50
Purchase #6	$246.60	10.836%	$273.3216	$273.32	$273.30	$273.30
Purchase #7	$59.30	5.544%	$62.5876	$62.59	$62.60	$62.60
7 purchase totals =	$708.30		$765.8448	$765.84	$765.90	$765.70