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	$156.85	7.454%	$168.5416	$168.54	$168.55	$168.50
Purchase #2	$107.69	13.712%	$122.4565	$122.46	$122.45	$122.50
Purchase #3	$86.81	12.631%	$97.775	$97.78	$97.80	$97.80
Purchase #4	$80.97	11.573%	$90.3407	$90.34	$90.35	$90.30
Purchase #5	$87.94	13.451%	$99.7688	$99.77	$99.75	$99.80
Purchase #6	$160.64	7.372%	$172.4824	$172.48	$172.50	$172.50
Purchase #7	$100.95	13.474%	$114.552	$114.55	$114.55	$114.60
7 purchase totals =	$781.85		$865.9170	$865.92	$865.95	$866.00