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	$29.27	10.789%	$32.4279	$32.43	$32.45	$32.40
Purchase #2	$212.56	4.827%	$222.8203	$222.82	$222.80	$222.80
Purchase #3	$153.39	9.849%	$168.4974	$168.50	$168.50	$168.50
Purchase #4	$59.61	12.676%	$67.1662	$67.17	$67.15	$67.20
Purchase #5	$33.61	5.580%	$35.4854	$35.49	$35.50	$35.50
Purchase #6	$163.45	7.632%	$175.9245	$175.92	$175.90	$175.90
Purchase #7	$102.86	12.604%	$115.8245	$115.82	$115.80	$115.80
7 purchase totals =	$754.75		$818.1462	$818.15	$818.10	$818.10