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	$44.61	13.102%	$50.4548	$50.45	$50.45	$50.50
Purchase #2	$234.26	10.764%	$259.4757	$259.48	$259.50	$259.50
Purchase #3	$39.71	3.216%	$40.9871	$40.99	$41.00	$41.00
Purchase #4	$182.50	7.587%	$196.3463	$196.35	$196.35	$196.30
Purchase #5	$56.82	4.136%	$59.1701	$59.17	$59.15	$59.20
Purchase #6	$109.98	8.177%	$118.9731	$118.97	$118.95	$119.00
Purchase #7	$30.66	9.683%	$33.6288	$33.63	$33.65	$33.60
7 purchase totals =	$698.54		$759.0359	$759.04	$759.05	$759.10