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	$20.62	6.122%	$21.8824	$21.88	$21.90	$21.90
Purchase #2	$112.61	13.443%	$127.7482	$127.75	$127.75	$127.70
Purchase #3	$51.90	7.645%	$55.8678	$55.87	$55.85	$55.90
Purchase #4	$74.57	13.257%	$84.4557	$84.46	$84.45	$84.50
Purchase #5	$135.39	13.278%	$153.3671	$153.37	$153.35	$153.40
Purchase #6	$85.86	4.460%	$89.6894	$89.69	$89.70	$89.70
Purchase #7	$20.94	4.672%	$21.9183	$21.92	$21.90	$21.90
7 purchase totals =	$501.89		$554.9289	$554.94	$554.90	$555.00