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	$166.67	3.437%	$172.3984	$172.40	$172.40	$172.40
Purchase #2	$187.45	12.215%	$210.347	$210.35	$210.35	$210.30
Purchase #3	$50.90	4.772%	$53.3289	$53.33	$53.35	$53.30
Purchase #4	$15.60	11.141%	$17.338	$17.34	$17.35	$17.30
Purchase #5	$69.65	4.273%	$72.6261	$72.63	$72.65	$72.60
Purchase #6	$169.69	12.806%	$191.4205	$191.42	$191.40	$191.40
Purchase #7	$48.49	12.370%	$54.4882	$54.49	$54.50	$54.50
7 purchase totals =	$708.45		$771.9471	$771.96	$772.00	$771.80