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	$120.98	10.722%	$133.9515	$133.95	$133.95	$134.00
Purchase #2	$186.77	5.685%	$197.3879	$197.39	$197.40	$197.40
Purchase #3	$147.49	3.758%	$153.0327	$153.03	$153.05	$153.00
Purchase #4	$41.41	10.259%	$45.6583	$45.66	$45.65	$45.70
Purchase #5	$89.38	11.321%	$99.4987	$99.50	$99.50	$99.50
Purchase #6	$68.73	4.603%	$71.8936	$71.89	$71.90	$71.90
Purchase #7	$16.99	6.200%	$18.0434	$18.04	$18.05	$18.00
7 purchase totals =	$671.75		$719.4661	$719.46	$719.50	$719.50