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	$170.77	4.358%	$178.2122	$178.21	$178.20	$178.20
Purchase #2	$87.53	5.746%	$92.5595	$92.56	$92.55	$92.60
Purchase #3	$162.57	12.423%	$182.7661	$182.77	$182.75	$182.80
Purchase #4	$158.27	11.438%	$176.3729	$176.37	$176.35	$176.40
Purchase #5	$63.91	5.689%	$67.5458	$67.55	$67.55	$67.50
Purchase #6	$128.53	10.829%	$142.4485	$142.45	$142.45	$142.40
Purchase #7	$94.51	5.360%	$99.5757	$99.58	$99.60	$99.60
7 purchase totals =	$866.09		$939.4807	$939.49	$939.45	$939.50