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	$206.91	6.561%	$220.4854	$220.49	$220.50	$220.50
Purchase #2	$250.64	9.555%	$274.5887	$274.59	$274.60	$274.60
Purchase #3	$73.86	6.309%	$78.5198	$78.52	$78.50	$78.50
Purchase #4	$122.32	13.440%	$138.7598	$138.76	$138.75	$138.80
Purchase #5	$9.89	3.337%	$10.22	$10.22	$10.20	$10.20
Purchase #6	$80.50	6.638%	$85.8436	$85.84	$85.85	$85.80
Purchase #7	$73.77	10.218%	$81.3078	$81.31	$81.30	$81.30
7 purchase totals =	$817.89		$889.7251	$889.73	$889.70	$889.70