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	$44.88	5.520%	$47.3574	$47.36	$47.35	$47.40
Purchase #2	$83.59	8.400%	$90.6116	$90.61	$90.60	$90.60
Purchase #3	$29.86	12.376%	$33.5555	$33.56	$33.55	$33.60
Purchase #4	$193.46	3.663%	$200.5464	$200.55	$200.55	$200.50
Purchase #5	$53.78	4.836%	$56.3808	$56.38	$56.40	$56.40
Purchase #6	$97.72	11.612%	$109.0672	$109.07	$109.05	$109.10
Purchase #7	$50.84	4.746%	$53.2529	$53.25	$53.25	$53.30
7 purchase totals =	$554.13		$590.7718	$590.78	$590.75	$590.90