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	$174.46	8.797%	$189.8072	$189.81	$189.80	$189.80
Purchase #2	$87.46	6.185%	$92.8694	$92.87	$92.85	$92.90
Purchase #3	$48.97	11.172%	$54.4409	$54.44	$54.45	$54.40
Purchase #4	$245.43	13.679%	$279.0024	$279.00	$279.00	$279.00
Purchase #5	$7.71	11.410%	$8.5897	$8.59	$8.60	$8.60
Purchase #6	$48.59	4.829%	$50.9364	$50.94	$50.95	$50.90
Purchase #7	$43.70	3.501%	$45.2299	$45.23	$45.25	$45.20
7 purchase totals =	$656.32		$720.8759	$720.88	$720.90	$720.80