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	$137.87	6.770%	$147.2038	$147.20	$147.20	$147.20
Purchase #2	$23.98	3.446%	$24.8064	$24.81	$24.80	$24.80
Purchase #3	$115.83	9.752%	$127.1257	$127.13	$127.15	$127.10
Purchase #4	$50.32	6.285%	$53.4826	$53.48	$53.50	$53.50
Purchase #5	$68.71	11.457%	$76.5821	$76.58	$76.60	$76.60
Purchase #6	$41.94	7.674%	$45.1585	$45.16	$45.15	$45.20
Purchase #7	$102.66	8.857%	$111.7526	$111.75	$111.75	$111.80
7 purchase totals =	$541.31		$586.1117	$586.11	$586.15	$586.20