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	$15.88	6.597%	$16.9276	$16.93	$16.95	$16.90
Purchase #2	$100.32	4.700%	$105.035	$105.04	$105.05	$105.00
Purchase #3	$169.47	11.836%	$189.5285	$189.53	$189.55	$189.50
Purchase #4	$110.70	11.354%	$123.2689	$123.27	$123.25	$123.30
Purchase #5	$218.69	12.150%	$245.2608	$245.26	$245.25	$245.30
Purchase #6	$109.88	11.131%	$122.1107	$122.11	$122.10	$122.10
Purchase #7	$38.56	13.759%	$43.8655	$43.87	$43.85	$43.90
7 purchase totals =	$763.50		$845.9970	$846.01	$846.00	$846.00