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	$109.86	12.315%	$123.3893	$123.39	$123.40	$123.40
Purchase #2	$9.36	11.261%	$10.414	$10.41	$10.40	$10.40
Purchase #3	$38.47	11.611%	$42.9368	$42.94	$42.95	$42.90
Purchase #4	$51.38	11.735%	$57.4094	$57.41	$57.40	$57.40
Purchase #5	$42.62	4.753%	$44.6457	$44.65	$44.65	$44.60
Purchase #6	$50.70	3.481%	$52.4649	$52.46	$52.45	$52.50
Purchase #7	$12.67	12.601%	$14.2665	$14.27	$14.25	$14.30
7 purchase totals =	$315.06		$345.5266	$345.53	$345.50	$345.50