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	$121.27	8.158%	$131.1632	$131.16	$131.15	$131.20
Purchase #2	$30.90	6.536%	$32.9196	$32.92	$32.90	$32.90
Purchase #3	$11.29	4.645%	$11.8144	$11.81	$11.80	$11.80
Purchase #4	$126.80	12.457%	$142.5955	$142.60	$142.60	$142.60
Purchase #5	$52.68	12.296%	$59.1575	$59.16	$59.15	$59.20
Purchase #6	$46.87	9.273%	$51.2163	$51.22	$51.20	$51.20
Purchase #7	$99.52	12.351%	$111.8117	$111.81	$111.80	$111.80
7 purchase totals =	$489.33		$540.6782	$540.68	$540.60	$540.70