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	$198.54	12.256%	$222.8731	$222.87	$222.85	$222.90
Purchase #2	$237.56	3.524%	$245.9316	$245.93	$245.95	$245.90
Purchase #3	$161.60	5.389%	$170.3086	$170.31	$170.30	$170.30
Purchase #4	$39.71	10.688%	$43.9542	$43.95	$43.95	$44.00
Purchase #5	$148.49	7.262%	$159.2733	$159.27	$159.25	$159.30
Purchase #6	$70.26	11.674%	$78.4622	$78.46	$78.45	$78.50
Purchase #7	$52.27	13.565%	$59.3604	$59.36	$59.35	$59.40
7 purchase totals =	$908.43		$980.1634	$980.15	$980.10	$980.30