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	$241.68	11.592%	$269.6955	$269.70	$269.70	$269.70
Purchase #2	$248.99	12.764%	$280.7711	$280.77	$280.75	$280.80
Purchase #3	$139.96	3.123%	$144.331	$144.33	$144.35	$144.30
Purchase #4	$114.89	4.755%	$120.353	$120.35	$120.35	$120.40
Purchase #5	$115.28	12.424%	$129.6024	$129.60	$129.60	$129.60
Purchase #6	$132.83	3.326%	$137.2479	$137.25	$137.25	$137.20
Purchase #7	$87.83	12.584%	$98.8825	$98.88	$98.90	$98.90
7 purchase totals =	$1,081.46		$1,180.8834	$1,180.88	$1,180.90	$1,180.90