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	$243.26	12.796%	$274.3875	$274.39	$274.40	$274.40
Purchase #2	$180.52	11.268%	$200.861	$200.86	$200.85	$200.90
Purchase #3	$45.36	13.563%	$51.5122	$51.51	$51.50	$51.50
Purchase #4	$121.60	3.114%	$125.3866	$125.39	$125.40	$125.40
Purchase #5	$141.32	6.301%	$150.2246	$150.22	$150.20	$150.20
Purchase #6	$126.93	4.242%	$132.3144	$132.31	$132.30	$132.30
Purchase #7	$80.94	3.139%	$83.4807	$83.48	$83.50	$83.50
7 purchase totals =	$939.93		$1,018.1670	$1,018.16	$1,018.15	$1,018.20