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	$42.96	6.661%	$45.8216	$45.82	$45.80	$45.80
Purchase #2	$91.42	12.627%	$102.9636	$102.96	$102.95	$103.00
Purchase #3	$179.87	9.336%	$196.6627	$196.66	$196.65	$196.70
Purchase #4	$147.67	9.139%	$161.1656	$161.17	$161.15	$161.20
Purchase #5	$29.96	7.542%	$32.2196	$32.22	$32.20	$32.20
Purchase #6	$107.31	4.284%	$111.9072	$111.91	$111.90	$111.90
Purchase #7	$138.56	12.610%	$156.0324	$156.03	$156.05	$156.00
7 purchase totals =	$737.75		$806.7727	$806.77	$806.70	$806.80