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	$248.28	13.128%	$280.8742	$280.87	$280.85	$280.90
Purchase #2	$226.37	13.303%	$256.484	$256.48	$256.50	$256.50
Purchase #3	$190.72	7.110%	$204.2802	$204.28	$204.30	$204.30
Purchase #4	$84.94	6.354%	$90.3371	$90.34	$90.35	$90.30
Purchase #5	$212.30	5.585%	$224.157	$224.16	$224.15	$224.20
Purchase #6	$80.43	7.221%	$86.2379	$86.24	$86.25	$86.20
Purchase #7	$116.85	9.633%	$128.1062	$128.11	$128.10	$128.10
7 purchase totals =	$1,159.89		$1,270.4766	$1,270.48	$1,270.50	$1,270.50