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	$136.74	9.541%	$149.7864	$149.79	$149.80	$149.80
Purchase #2	$52.63	13.700%	$59.8403	$59.84	$59.85	$59.80
Purchase #3	$86.93	4.620%	$90.9462	$90.95	$90.95	$90.90
Purchase #4	$29.34	12.779%	$33.0894	$33.09	$33.10	$33.10
Purchase #5	$249.71	13.748%	$284.0401	$284.04	$284.05	$284.00
Purchase #6	$143.64	3.702%	$148.9576	$148.96	$148.95	$149.00
Purchase #7	$103.82	5.702%	$109.7398	$109.74	$109.75	$109.70
7 purchase totals =	$802.81		$876.3998	$876.41	$876.45	$876.30