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	$53.68	10.658%	$59.4012	$59.40	$59.40	$59.40
Purchase #2	$5.80	9.218%	$6.3346	$6.33	$6.35	$6.30
Purchase #3	$85.77	11.845%	$95.9295	$95.93	$95.95	$95.90
Purchase #4	$245.57	13.622%	$279.0215	$279.02	$279.00	$279.00
Purchase #5	$31.88	6.307%	$33.8907	$33.89	$33.90	$33.90
Purchase #6	$20.92	4.168%	$21.7919	$21.79	$21.80	$21.80
Purchase #7	$139.73	12.336%	$156.9671	$156.97	$156.95	$157.00
7 purchase totals =	$583.35		$653.3365	$653.33	$653.35	$653.30