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	$79.90	7.368%	$85.787	$85.79	$85.80	$85.80
Purchase #2	$247.75	3.632%	$256.7483	$256.75	$256.75	$256.70
Purchase #3	$241.38	12.412%	$271.3401	$271.34	$271.35	$271.30
Purchase #4	$77.90	5.360%	$82.0754	$82.08	$82.10	$82.10
Purchase #5	$72.25	10.229%	$79.6405	$79.64	$79.65	$79.60
Purchase #6	$87.45	5.358%	$92.1356	$92.14	$92.15	$92.10
Purchase #7	$30.37	4.149%	$31.6301	$31.63	$31.65	$31.60
7 purchase totals =	$837.00		$899.3570	$899.37	$899.45	$899.20