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	$6.46	5.554%	$6.8188	$6.82	$6.80	$6.80
Purchase #2	$219.82	11.234%	$244.5146	$244.51	$244.50	$244.50
Purchase #3	$72.84	12.861%	$82.208	$82.21	$82.20	$82.20
Purchase #4	$113.98	9.794%	$125.1432	$125.14	$125.15	$125.10
Purchase #5	$99.27	12.407%	$111.5864	$111.59	$111.60	$111.60
Purchase #6	$62.32	7.162%	$66.7834	$66.78	$66.80	$66.80
Purchase #7	$218.36	12.753%	$246.2075	$246.21	$246.20	$246.20
7 purchase totals =	$793.05		$883.2619	$883.26	$883.25	$883.20