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	$155.38	6.403%	$165.329	$165.33	$165.35	$165.30
Purchase #2	$249.85	3.768%	$259.2643	$259.26	$259.25	$259.30
Purchase #3	$131.36	9.429%	$143.7459	$143.75	$143.75	$143.70
Purchase #4	$218.62	10.298%	$241.1335	$241.13	$241.15	$241.10
Purchase #5	$208.29	10.369%	$229.8876	$229.89	$229.90	$229.90
Purchase #6	$222.54	6.689%	$237.4257	$237.43	$237.45	$237.40
Purchase #7	$100.67	8.524%	$109.2511	$109.25	$109.25	$109.30
7 purchase totals =	$1,286.71		$1,386.0371	$1,386.04	$1,386.10	$1,386.00