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	$99.29	12.690%	$111.8899	$111.89	$111.90	$111.90
Purchase #2	$83.64	13.469%	$94.9055	$94.91	$94.90	$94.90
Purchase #3	$47.88	6.614%	$51.0468	$51.05	$51.05	$51.00
Purchase #4	$146.29	5.631%	$154.5276	$154.53	$154.55	$154.50
Purchase #5	$152.59	12.634%	$171.8682	$171.87	$171.85	$171.90
Purchase #6	$77.81	9.831%	$85.4595	$85.46	$85.45	$85.50
Purchase #7	$158.49	7.157%	$169.8331	$169.83	$169.85	$169.80
7 purchase totals =	$765.99		$839.5306	$839.54	$839.55	$839.50