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	$138.42	8.642%	$150.3823	$150.38	$150.40	$150.40
Purchase #2	$45.66	13.807%	$51.9643	$51.96	$51.95	$52.00
Purchase #3	$143.98	8.815%	$156.6718	$156.67	$156.65	$156.70
Purchase #4	$176.32	7.830%	$190.1259	$190.13	$190.15	$190.10
Purchase #5	$84.94	5.686%	$89.7697	$89.77	$89.75	$89.80
Purchase #6	$134.52	11.121%	$149.48	$149.48	$149.50	$149.50
Purchase #7	$9.60	13.290%	$10.8758	$10.88	$10.90	$10.90
7 purchase totals =	$733.44		$799.2698	$799.27	$799.30	$799.40