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	$68.45	6.196%	$72.6912	$72.69	$72.70	$72.70
Purchase #2	$162.70	6.262%	$172.8883	$172.89	$172.90	$172.90
Purchase #3	$157.45	11.412%	$175.4182	$175.42	$175.40	$175.40
Purchase #4	$44.56	5.344%	$46.9413	$46.94	$46.95	$46.90
Purchase #5	$88.65	9.432%	$97.0115	$97.01	$97.00	$97.00
Purchase #6	$18.95	9.824%	$20.8116	$20.81	$20.80	$20.80
Purchase #7	$209.34	11.527%	$233.4706	$233.47	$233.45	$233.50
7 purchase totals =	$750.10		$819.2327	$819.23	$819.20	$819.20