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	$174.45	3.180%	$179.9975	$180.00	$180.00	$180.00
Purchase #2	$156.49	11.759%	$174.8917	$174.89	$174.90	$174.90
Purchase #3	$13.31	3.855%	$13.8231	$13.82	$13.80	$13.80
Purchase #4	$215.38	3.574%	$223.0777	$223.08	$223.10	$223.10
Purchase #5	$227.55	9.173%	$248.4232	$248.42	$248.40	$248.40
Purchase #6	$29.78	3.848%	$30.9259	$30.93	$30.95	$30.90
Purchase #7	$250.56	11.760%	$280.0259	$280.03	$280.05	$280.00
7 purchase totals =	$1,067.52		$1,151.1650	$1,151.17	$1,151.20	$1,151.10